1 (* ========================================================================= *)
2 (* Independence of the parallel postulate. The statement and some ideas are *)
3 (* taken from Tim Makarios's MSc thesis "A mechanical verification of the *)
4 (* independence of Tarski's Euclidean axiom". *)
6 (* In the file Multivariate/tarski.ml it is shown that all 11 of Tarski's *)
7 (* axioms for geometry hold for the Euclidean plane `:real^2`, with *)
8 (* betweenness and congruence of segments as: *)
10 (* B x y z <=> between y (x,z) *)
11 (* ab == pq <=> dist(a,b) = dist(p,q) *)
13 (* The present file shows that the Klein model of the hyperbolic plane (type *)
14 (* `:plane`) satisfies all Tarski's axioms except that it satisfies the *)
15 (* negation of the Euclidean axiom (10), with betweenness and congruence of *)
18 (* B x y z <=> pbetween y (x,z) *)
19 (* ab == pq <=> pdist(a,b) = pdist(p,q) *)
21 (* Collectively, these two results show that the Euclidean axiom is *)
22 (* independent of the others. For more references regarding Tarski's axioms *)
23 (* for geometry see "http://en.wikipedia.org/wiki/Tarski's_axioms". *)
24 (* ========================================================================= *)
26 needs "Multivariate/tarski.ml";;
27 needs "Multivariate/cauchy.ml";;
29 (* ------------------------------------------------------------------------- *)
30 (* The semimetric we will use, directly on real^N first. Choose a sensible *)
31 (* default outside unit ball so some handy theorems become unconditional. *)
32 (* ------------------------------------------------------------------------- *)
34 let mdist = new_definition
35 `mdist(x:real^N,y:real^N) =
36 if norm(x) < &1 /\ norm(y) < &1 then
37 (&1 - x dot y) pow 2 / ((&1 - norm(x) pow 2) * (&1 - norm(y) pow 2)) - &1
40 let MDIST_INCREASES_ONLINE = prove
42 norm a < &1 /\ norm b < &1 /\ norm x < &1 /\ between x (a,b) /\ ~(x = b)
43 ==> mdist(a,x) < mdist(a,b)`,
44 REPEAT STRIP_TAC THEN ASM_CASES_TAC `b:real^N = a` THENL
45 [ASM_MESON_TAC[BETWEEN_REFL_EQ]; ALL_TAC] THEN
46 ASM_SIMP_TAC[mdist; real_div; REAL_INV_MUL] THEN
48 `norm(a:real^N) pow 2 < &1 /\ norm(b:real^N) pow 2 < &1 /\
49 norm(x:real^N) pow 2 < &1`
50 MP_TAC THENL [ASM_SIMP_TAC[ABS_SQUARE_LT_1; REAL_ABS_NORM]; ALL_TAC] THEN
51 REWRITE_TAC[REAL_ARITH `a * inv x * inv b - &1 < c * inv x * d - &1 <=>
52 (a / b) / x < (c * d) / x`] THEN
53 SIMP_TAC[REAL_LT_DIV2_EQ; REAL_LT_LDIV_EQ; REAL_SUB_LT] THEN
54 ONCE_REWRITE_TAC[REAL_ARITH `(a * inv b) * c:real = (a * c) / b`] THEN
55 SIMP_TAC[REAL_LT_RDIV_EQ; REAL_SUB_LT] THEN
56 SUBGOAL_THEN `(a:real^N) dot b < &1 /\ (a:real^N) dot x < &1` MP_TAC THENL
57 [CONJ_TAC THEN MATCH_MP_TAC(MESON[REAL_LET_TRANS; NORM_CAUCHY_SCHWARZ]
58 `norm(x) * norm(y) < &1 ==> (x:real^N) dot y < &1`) THEN
59 GEN_REWRITE_TAC RAND_CONV [GSYM REAL_MUL_LID] THEN
60 MATCH_MP_TAC REAL_LT_MUL2 THEN ASM_REWRITE_TAC[NORM_POS_LE];
62 FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [BETWEEN_IN_SEGMENT]) THEN
63 REWRITE_TAC[IN_SEGMENT; LEFT_IMP_EXISTS_THM] THEN X_GEN_TAC `u:real` THEN
64 ASM_CASES_TAC `u = &1` THEN
65 ASM_SIMP_TAC[VECTOR_ARITH `(&1 - &1) % a + &1 % b:real^N = b`] THEN
66 STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
67 SIMP_TAC[VECTOR_ARITH `(&1 - u) % a + u % b:real^N = a + u % (b - a)`] THEN
68 ABBREV_TAC `c:real^N = b - a` THEN
69 SUBGOAL_THEN `b:real^N = a + c` SUBST_ALL_TAC THENL
70 [EXPAND_TAC "c" THEN VECTOR_ARITH_TAC; ALL_TAC] THEN
71 RULE_ASSUM_TAC(SIMP_RULE[VECTOR_ARITH `a + c:real^N = a <=> c = vec 0`]) THEN
72 REWRITE_TAC[NORM_POW_2; VECTOR_ARITH
73 `(a + b:real^N) dot (a + b) = a dot a + &2 * a dot b + b dot b`] THEN
74 REWRITE_TAC[DOT_RADD; DOT_RMUL] THEN REWRITE_TAC[DOT_LMUL] THEN
75 REPEAT STRIP_TAC THEN REWRITE_TAC[REAL_ARITH
76 `(&1 - (a + x * b)) pow 2 * (&1 - (a + &2 * b + c)) <
77 (&1 - (a + b)) pow 2 * (&1 - (a + &2 * x * b + x * x * c)) <=>
78 &0 < (&1 - a - b * x) * ((&1 - a) * c + b pow 2) * (&1 - x) +
79 (&1 - a - b) * ((&1 - a) * c + b pow 2) * (&1 - x) * x`] THEN
80 MATCH_MP_TAC REAL_LTE_ADD THEN CONJ_TAC THENL
81 [REPEAT(MATCH_MP_TAC REAL_LT_MUL THEN CONJ_TAC);
82 REPEAT(MATCH_MP_TAC REAL_LE_MUL THEN CONJ_TAC)] THEN
83 TRY ASM_REAL_ARITH_TAC THEN TRY(MATCH_MP_TAC REAL_LT_IMP_LE) THEN
84 MATCH_MP_TAC REAL_LTE_ADD THEN REWRITE_TAC[REAL_LE_POW_2] THEN
85 MATCH_MP_TAC REAL_LT_MUL THEN ASM_REWRITE_TAC[DOT_POS_LT; REAL_SUB_LT]);;
87 let MDIST_REFL = prove
88 (`!x:real^N. mdist(x,x) = &0`,
89 GEN_TAC THEN REWRITE_TAC[mdist; DIST_REFL; NORM_POW_2; NORM_LT_SQUARE] THEN
90 CONV_TAC REAL_FIELD);;
93 (`!x y:real^N. mdist(x,y) = mdist(y,x)`,
94 REWRITE_TAC[mdist; CONJ_ACI; REAL_MUL_AC; DIST_SYM; DOT_SYM]);;
96 let MDIST_POS_LT = prove
97 (`!x y:real^N. ~(x = y) ==> &0 < mdist(x,y)`,
99 ASM_CASES_TAC `norm(x:real^N) < &1 /\ norm(y:real^N) < &1` THENL
100 [ASM_MESON_TAC[MDIST_INCREASES_ONLINE; MDIST_REFL; BETWEEN_REFL];
101 ASM_SIMP_TAC[mdist; DIST_POS_LT]]);;
103 let MDIST_POS_LE = prove
104 (`!x y:real^N. &0 <= mdist(x,y)`,
105 REPEAT GEN_TAC THEN ASM_CASES_TAC `x:real^N = y` THEN
106 ASM_SIMP_TAC[MDIST_REFL; MDIST_POS_LT; REAL_LE_LT]);;
108 let MDIST_EQ_0 = prove
109 (`!x y:real^N. mdist(x,y) = &0 <=> x = y`,
110 MESON_TAC[MDIST_REFL; MDIST_POS_LT; REAL_LT_REFL]);;
112 let BETWEEN_COLLINEAR_MDIST_EQ = prove
114 norm(a) < &1 /\ norm(b) < &1 /\ norm(x) < &1
115 ==> (between x (a,b) <=>
116 collinear {a, x, b} /\
117 mdist(x,a) <= mdist (a,b) /\ mdist(x,b) <= mdist(a,b))`,
118 REPEAT GEN_TAC THEN STRIP_TAC THEN EQ_TAC THENL
119 [SIMP_TAC[BETWEEN_IMP_COLLINEAR];
120 REWRITE_TAC[COLLINEAR_BETWEEN_CASES]] THEN
121 ASM_MESON_TAC[MDIST_INCREASES_ONLINE; MDIST_SYM; REAL_LT_IMP_LE;
122 REAL_LE_REFL; BETWEEN_SYM; REAL_NOT_LE; BETWEEN_REFL]);;
124 let CONTINUOUS_AT_LIFT_MDIST = prove
126 norm(a) < &1 /\ norm(x) < &1 ==> (\x. lift(mdist(a,x))) continuous at x`,
127 REPEAT STRIP_TAC THEN MATCH_MP_TAC CONTINUOUS_TRANSFORM_AT THEN EXISTS_TAC
128 `\x:real^N. lift((&1 - a dot x) pow 2 /
129 ((&1 - norm a pow 2) * (&1 - norm x pow 2)) - &1)` THEN
130 EXISTS_TAC `&1 - norm(x:real^N)` THEN ASM_REWRITE_TAC[REAL_SUB_LT] THEN
132 [X_GEN_TAC `y:real^N` THEN DISCH_THEN(MP_TAC o MATCH_MP (NORM_ARITH
133 `dist(y,x) < &1 - norm x ==> norm y < &1`)) THEN ASM_SIMP_TAC[mdist];
134 REWRITE_TAC[LIFT_SUB; real_div; LIFT_CMUL; REAL_INV_MUL] THEN
135 MATCH_MP_TAC CONTINUOUS_SUB THEN SIMP_TAC[CONTINUOUS_CONST] THEN
136 REPEAT(MATCH_MP_TAC CONTINUOUS_MUL THEN CONJ_TAC) THEN
137 SIMP_TAC[CONTINUOUS_CONST; o_DEF; REAL_POW_2; LIFT_CMUL] THENL
138 [MATCH_MP_TAC(REWRITE_RULE[o_DEF] CONTINUOUS_MUL);
139 MATCH_MP_TAC(REWRITE_RULE[o_DEF] CONTINUOUS_AT_INV)] THEN
140 ASM_SIMP_TAC[REAL_ARITH `x < &1 * &1 ==> ~(&1 - x = &0)`; REAL_LT_MUL2;
141 NORM_POS_LE; LIFT_SUB] THEN
142 SIMP_TAC[GSYM REAL_POW_2; NORM_POW_2; CONTINUOUS_CONST; CONTINUOUS_AT_ID;
143 CONTINUOUS_SUB; CONTINUOUS_LIFT_DOT2]]);;
145 let HYPERBOLIC_MIDPOINT = prove
147 norm a < &1 /\ norm b < &1
148 ==> ?x. between x (a,b) /\ mdist(x,a) = mdist(x,b)`,
149 REPEAT STRIP_TAC THEN MP_TAC(ISPECL
150 [`\x:real^N. lift(mdist(x,a) - mdist(x,b))`; `segment[a:real^N,b]`]
151 CONNECTED_CONTINUOUS_IMAGE) THEN
153 [REWRITE_TAC[CONNECTED_SEGMENT; LIFT_SUB] THEN
154 MATCH_MP_TAC CONTINUOUS_AT_IMP_CONTINUOUS_ON THEN REPEAT STRIP_TAC THEN
155 MATCH_MP_TAC CONTINUOUS_SUB THEN ONCE_REWRITE_TAC[MDIST_SYM] THEN
156 CONJ_TAC THEN MATCH_MP_TAC CONTINUOUS_AT_LIFT_MDIST THEN
157 ASM_MESON_TAC[BETWEEN_NORM_LT; BETWEEN_IN_SEGMENT];
158 REWRITE_TAC[GSYM IS_INTERVAL_CONNECTED_1; IS_INTERVAL_1] THEN
159 REWRITE_TAC[IMP_CONJ; RIGHT_FORALL_IMP_THM; FORALL_IN_IMAGE] THEN
160 REWRITE_TAC[IMP_IMP; RIGHT_IMP_FORALL_THM; LIFT_DROP] THEN
161 DISCH_THEN(MP_TAC o SPECL [`a:real^N`; `b:real^N`; `lift(&0)`]) THEN
162 ASM_SIMP_TAC[MDIST_REFL; LIFT_DROP; ENDS_IN_SEGMENT; IN_IMAGE] THEN
163 REWRITE_TAC[REAL_SUB_RZERO; REAL_ARITH `&0 - x <= &0 <=> &0 <= x`] THEN
164 ASM_SIMP_TAC[MDIST_POS_LE; LIFT_EQ; BETWEEN_IN_SEGMENT] THEN
165 ASM_MESON_TAC[REAL_SUB_0; MDIST_SYM]]);;
167 let MDIST_EQ_ORIGIN = prove
168 (`!x:real^N y:real^N.
169 norm x < &1 /\ norm y < &1
170 ==> (mdist(vec 0,x) = mdist(vec 0,y) <=> norm x = norm y)`,
171 REPEAT STRIP_TAC THEN ASM_SIMP_TAC[mdist; NORM_0; REAL_LT_01] THEN
172 REWRITE_TAC[DOT_LZERO] THEN CONV_TAC REAL_RAT_REDUCE_CONV THEN
173 REWRITE_TAC[real_div; REAL_MUL_LID; REAL_EQ_INV2;
174 REAL_ARITH `x - &1 = y - &1 <=> x = y`] THEN
175 REWRITE_TAC[REAL_ARITH `&1 - x = &1 - y <=> x = y`;
176 GSYM REAL_EQ_SQUARE_ABS; REAL_ABS_NORM]);;
178 let MDIST_CONGRUENT_TRIPLES_0 = prove
179 (`!a b:real^N a' b':real^N.
180 norm a < &1 /\ norm b < &1 /\ norm a' < &1 /\ norm b' < &1
181 ==> (mdist(vec 0,a) = mdist(vec 0,a') /\ mdist(a,b) = mdist(a',b') /\
182 mdist(b,vec 0) = mdist(b',vec 0) <=>
183 dist(vec 0,a) = dist(vec 0,a') /\ dist(a,b) = dist(a',b') /\
184 dist(b,vec 0) = dist(b',vec 0))`,
185 REPEAT STRIP_TAC THEN
186 ASM_SIMP_TAC[MDIST_EQ_ORIGIN; REWRITE_RULE[MDIST_SYM] MDIST_EQ_ORIGIN] THEN
187 REWRITE_TAC[DIST_0; NORM_0; REAL_LT_01] THEN MATCH_MP_TAC(TAUT
188 `(a /\ b ==> (x <=> y)) ==> (a /\ x /\ b <=> a /\ y /\ b)`) THEN
189 STRIP_TAC THEN ASM_SIMP_TAC[mdist; DIST_EQ; real_div; REAL_INV_MUL; REAL_RING
190 `x * a * b - &1 = y * a * b - &1 <=> x = y \/ a = &0 \/ b = &0`] THEN
191 REWRITE_TAC[dist; NORM_POW_2; DOT_LSUB; DOT_RSUB; DOT_SYM] THEN
192 REWRITE_TAC[GSYM REAL_EQ_SQUARE_ABS; NORM_POW_2] THEN
193 ASM_SIMP_TAC[REAL_INV_EQ_0; real_abs; REAL_SUB_LE; REAL_SUB_0] THEN
194 ASM_SIMP_TAC[ABS_SQUARE_LT_1; REAL_ABS_NORM; REAL_LT_IMP_NE; REAL_LT_IMP_LE;
195 MESON[NORM_CAUCHY_SCHWARZ; REAL_LET_TRANS; NORM_POS_LE;
196 REAL_LT_MUL2; REAL_MUL_RID; REAL_LT_IMP_LE]
197 `norm x < &1 /\ norm y < &1 ==> x dot y < &1`] THEN
198 RULE_ASSUM_TAC(REWRITE_RULE[NORM_EQ]) THEN ASM_REAL_ARITH_TAC);;
200 (* ------------------------------------------------------------------------- *)
201 (* Deduce existence of hyperbolic translations via the Poincare disc model. *)
202 (* Use orthogonal projection onto a hemisphere touching the unit disc, *)
203 (* then stereographic projection back from the other pole of the sphere plus *)
204 (* scaling. See Greenberg's "Euclidean & Non-Euclidean Geometries" fig 7.13. *)
205 (* ------------------------------------------------------------------------- *)
207 let kleinify = new_definition
208 `kleinify z = Cx(&2 / (&1 + norm(z) pow 2)) * z`;;
210 let poincarify = new_definition
211 `poincarify x = Cx((&1 - sqrt(&1 - norm(x) pow 2)) / norm(x) pow 2) * x`;;
213 let KLEINIFY_0,POINCARIFY_0 = (CONJ_PAIR o prove)
214 (`kleinify (Cx(&0)) = Cx(&0) /\ poincarify (Cx(&0)) = Cx(&0)`,
215 REWRITE_TAC[kleinify; poincarify; COMPLEX_MUL_RZERO]);;
217 let NORM_KLEINIFY = prove
218 (`!z. norm(kleinify z) = (&2 * norm(z)) / (&1 + norm(z) pow 2)`,
219 REWRITE_TAC[kleinify; COMPLEX_NORM_MUL; COMPLEX_NORM_CX; REAL_ABS_DIV] THEN
220 SIMP_TAC[REAL_LE_POW_2; REAL_ARITH `&0 <= x ==> abs(&1 + x) = &1 + x`] THEN
223 let NORM_KLEINIFY_LT = prove
224 (`!z. norm(kleinify z) < &1 <=> ~(norm z = &1)`,
225 ASM_SIMP_TAC[NORM_KLEINIFY; REAL_LE_POW_2; REAL_LT_LDIV_EQ; REAL_MUL_LID;
226 REAL_ARITH `&0 <= x ==> &0 < &1 + x`] THEN
227 SIMP_TAC[REAL_ARITH `&2 * z < (&1 + z pow 2) <=> &0 < (z - &1) pow 2`] THEN
228 REWRITE_TAC[REAL_POW_2; REAL_LT_SQUARE] THEN REAL_ARITH_TAC);;
230 let NORM_POINCARIFY_LT = prove
231 (`!x. norm(x) < &1 ==> norm(poincarify x) < &1`,
232 REPEAT STRIP_TAC THEN REWRITE_TAC[poincarify; COMPLEX_NORM_MUL] THEN
233 MATCH_MP_TAC(REAL_ARITH `x * y <= &1 * y /\ y < &1 ==> x * y < &1`) THEN
234 ASM_REWRITE_TAC[] THEN MATCH_MP_TAC REAL_LE_RMUL THEN
235 REWRITE_TAC[NORM_POS_LE; COMPLEX_NORM_MUL; COMPLEX_NORM_CX] THEN
236 REWRITE_TAC[REAL_ABS_DIV; REAL_ABS_NORM; REAL_ABS_POW] THEN
237 ASM_CASES_TAC `x:real^2 = vec 0` THEN
238 ASM_SIMP_TAC[REAL_LE_LDIV_EQ; NORM_POS_LT; REAL_POW_LT; NORM_0] THENL
239 [REAL_ARITH_TAC; REWRITE_TAC[REAL_MUL_LID]] THEN
240 MATCH_MP_TAC(REAL_ARITH `s <= &1 /\ &1 - x <= s ==> abs(&1 - s) <= x`) THEN
241 CONJ_TAC THENL [MATCH_MP_TAC REAL_LE_LSQRT; MATCH_MP_TAC REAL_LE_RSQRT] THEN
242 REWRITE_TAC[REAL_SUB_LE; REAL_POS; REAL_MUL_LID; REAL_POW_ONE] THEN
243 ASM_SIMP_TAC[REAL_ARITH `(&1 - x) pow 2 <= &1 - x <=> &0 <= x * (&1 - x)`;
244 REAL_ARITH `&1 - x <= &1 <=> &0 <= x`; REAL_LE_MUL; REAL_POW_LE;
245 REAL_SUB_LE; ABS_SQUARE_LE_1; REAL_LT_IMP_LE; REAL_ABS_NORM; NORM_POS_LE]);;
247 let KLEINIFY_POINCARIFY = prove
248 (`!x. norm(x) < &1 ==> kleinify(poincarify x) = x`,
249 REPEAT STRIP_TAC THEN REWRITE_TAC[kleinify; poincarify] THEN MATCH_MP_TAC
250 (COMPLEX_RING `(~(x = Cx(&0)) ==> w * z = Cx(&1)) ==> w * z * x = x`) THEN
251 DISCH_TAC THEN REWRITE_TAC[GSYM CX_MUL; CX_INJ; COMPLEX_NORM_MUL] THEN
252 REWRITE_TAC[COMPLEX_NORM_CX; REAL_ABS_DIV; REAL_ABS_NORM; REAL_ABS_POW] THEN
253 ASM_SIMP_TAC[COMPLEX_NORM_ZERO; REAL_FIELD
255 ==> (&1 + (a / y pow 2 * y) pow 2) = (y pow 2 + a pow 2) / y pow 2`] THEN
256 REWRITE_TAC[REAL_POW2_ABS; real_div; REAL_INV_MUL; REAL_INV_INV] THEN
257 ASM_SIMP_TAC[COMPLEX_NORM_ZERO; REAL_FIELD
258 `~(y = &0) ==> (&2 * x * y pow 2) * z * inv(y pow 2) = &2 * x * z`] THEN
259 MATCH_MP_TAC(REAL_FIELD `&0 < y /\ &2 * y = x ==> &2 * inv(x) * y = &1`) THEN
261 [REWRITE_TAC[REAL_SUB_LT] THEN MATCH_MP_TAC REAL_LT_LSQRT THEN
262 REWRITE_TAC[REAL_POS; REAL_ARITH `&1 - x < &1 pow 2 <=> &0 < x`] THEN
263 ASM_SIMP_TAC[REAL_POW_LT; COMPLEX_NORM_NZ];
264 SUBGOAL_THEN `sqrt(&1 - norm(x:real^2) pow 2) pow 2 = &1 - norm x pow 2`
265 MP_TAC THENL [MATCH_MP_TAC SQRT_POW_2; CONV_TAC REAL_FIELD]] THEN
266 ASM_SIMP_TAC[REAL_SUB_LE; ABS_SQUARE_LE_1; REAL_ABS_NORM; REAL_LT_IMP_LE]);;
268 let POINCARIFY_KLEINIFY = prove
269 (`!x. norm(x) < &1 ==> poincarify(kleinify x) = x`,
270 REPEAT STRIP_TAC THEN REWRITE_TAC[kleinify; poincarify] THEN
271 MATCH_MP_TAC(COMPLEX_RING
272 `(~(x = Cx(&0)) ==> w * z = Cx(&1)) ==> w * z * x = x`) THEN
273 DISCH_TAC THEN REWRITE_TAC[GSYM CX_MUL; CX_INJ] THEN
274 REWRITE_TAC[COMPLEX_NORM_MUL; COMPLEX_NORM_CX] THEN
275 REWRITE_TAC[REAL_ABS_DIV; REAL_ABS_NORM; REAL_ABS_POW; REAL_ABS_NUM] THEN
276 REWRITE_TAC[real_div; REAL_INV_MUL; REAL_INV_INV; GSYM REAL_MUL_ASSOC;
277 REAL_INV_POW; REAL_POW_MUL] THEN
278 MATCH_MP_TAC(REAL_FIELD
279 `~(c = &0) /\ abs d < &1 /\ a * b = &2 * c pow 2 * (&1 + d)
280 ==> a * inv(&2) pow 2 * b * inv(c) pow 2 * &2 * inv(&1 + d) = &1`) THEN
281 ASM_REWRITE_TAC[REAL_ABS_POW; COMPLEX_NORM_ZERO; ABS_SQUARE_LT_1] THEN
282 ASM_SIMP_TAC[REAL_ABS_NORM; REAL_POW_LE; NORM_POS_LE; REAL_ARITH
283 `&0 <= x ==> abs(&1 + x) = &1 + x`] THEN
284 MATCH_MP_TAC(REAL_FIELD
285 `~(x = &0) /\ abs x < &1 /\ a = &2 * x / (&1 + x)
286 ==> a * (&1 + x) pow 2 = &2 * x * (&1 + x)`) THEN
287 ASM_REWRITE_TAC[REAL_ABS_NORM; COMPLEX_NORM_ZERO; REAL_ABS_POW;
288 ABS_SQUARE_LT_1; REAL_POW_EQ_0] THEN
289 MATCH_MP_TAC(REAL_ARITH `x = &1 - y ==> &1 - x = y`) THEN
290 MATCH_MP_TAC SQRT_UNIQUE THEN
291 REWRITE_TAC[REAL_ARITH `&0 <= &1 - &2 * x / y <=> (&2 * x) / y <= &1`] THEN
292 SIMP_TAC[REAL_LE_LDIV_EQ; REAL_POW_LE; NORM_POS_LE; REAL_ARITH
293 `&0 <= x ==> &0 < &1 + x`] THEN
294 REWRITE_TAC[REAL_ARITH `&2 * x <= &1 * (&1 + x) <=> x <= &1`] THEN
295 ASM_SIMP_TAC[ABS_SQUARE_LE_1; REAL_ABS_NORM; REAL_LT_IMP_LE] THEN
296 SUBGOAL_THEN `~(&1 + norm(x:complex) pow 2 = &0)` MP_TAC THENL
297 [ALL_TAC; CONV_TAC REAL_FIELD] THEN
298 MATCH_MP_TAC(REAL_ARITH `abs(x) < &1 ==> ~(&1 + x = &0)`) THEN
299 ASM_REWRITE_TAC[REAL_ABS_POW; REAL_ABS_NORM; ABS_SQUARE_LT_1]);;
301 let MDIST_KLEINIFY = prove
302 (`!w z. ~(norm w = &1) /\ ~(norm z = &1)
303 ==> mdist(kleinify w,kleinify z) =
304 &4 * (&1 / &2 + norm(w - z) pow 2 /
305 ((&1 - norm w pow 2) * (&1 - norm z pow 2))) pow 2
307 REPEAT STRIP_TAC THEN MATCH_MP_TAC EQ_TRANS THEN EXISTS_TAC
308 `(&4 * norm(w - z:real^2) pow 2 *
309 ((&1 - norm w pow 2) * (&1 - norm z pow 2) + norm(w - z) pow 2)) /
310 ((&1 - norm w pow 2) pow 2 * (&1 - norm z pow 2) pow 2)` THEN
312 [ASM_SIMP_TAC[mdist; NORM_KLEINIFY_LT] THEN MATCH_MP_TAC(REAL_FIELD
313 `~(y = &0) /\ z = (w + &1) * y ==> z / y - &1 = w`) THEN
315 [REWRITE_TAC[REAL_ENTIRE; DE_MORGAN_THM] THEN CONJ_TAC THEN
316 MATCH_MP_TAC (REAL_ARITH `x < &1 ==> ~(&1 - x = &0)`) THEN
317 ASM_SIMP_TAC[REAL_POW_1_LT; NORM_KLEINIFY_LT; NORM_POS_LE; ARITH];
318 REWRITE_TAC[kleinify; COMPLEX_NORM_MUL; COMPLEX_NORM_CX] THEN
319 REWRITE_TAC[GSYM COMPLEX_CMUL; DOT_LMUL] THEN REWRITE_TAC[DOT_RMUL] THEN
320 SIMP_TAC[REAL_ABS_DIV; REAL_ABS_NUM; REAL_POW_LE; NORM_POS_LE;
321 REAL_ARITH `&0 <= x ==> abs(&1 + x) = &1 + x`] THEN
322 MATCH_MP_TAC(REAL_FIELD
323 `(~(y' = &0) /\ ~(y = &0)) /\
324 (y * y' - &4 * d) pow 2 =
325 b * (y pow 2 - &4 * x pow 2) * (y' pow 2 - &4 * x' pow 2)
326 ==> (&1 - &2 / y * &2 / y' * d) pow 2 =
327 b * (&1 - (&2 / y * x) pow 2) * (&1 - (&2 / y' * x') pow 2)`) THEN
330 MATCH_MP_TAC(REAL_ARITH `~(abs x = &1) ==> ~(&1 + x = &0)`) THEN
331 ASM_SIMP_TAC[REAL_ABS_POW; REAL_POW_EQ_1; REAL_ABS_NORM] THEN ARITH_TAC;
332 REWRITE_TAC[REAL_RING `(&1 + x) pow 2 - &4 * x = (&1 - x) pow 2`] THEN
333 MATCH_MP_TAC(REAL_FIELD
334 `(~(y = &0) /\ ~(y' = &0)) /\ a - y * y' = b
335 ==> a = (b / (y * y') + &1) * y * y'`) THEN
337 [ASM_REWRITE_TAC[REAL_POW_EQ_0; REAL_POW_EQ_1; REAL_ABS_NORM; ARITH;
338 REAL_ARITH `&1 - x = &0 <=> x = &1`];
339 REWRITE_TAC[NORM_POW_2; DOT_LSUB; DOT_RSUB; DOT_SYM] THEN
341 REPEAT(POP_ASSUM MP_TAC) THEN
342 REWRITE_TAC[NORM_EQ_SQUARE; GSYM NORM_POW_2] THEN CONV_TAC REAL_FIELD]);;
344 let MDIST_KLEINIFY_EQ = prove
346 ~(norm w = &1) /\ ~(norm z = &1) /\ ~(norm w' = &1) /\ ~(norm z' = &1) /\
347 norm(w - z) pow 2 * (&1 - norm w' pow 2) * (&1 - norm z' pow 2) =
348 norm(w' - z') pow 2 * (&1 - norm w pow 2) * (&1 - norm z pow 2)
349 ==> mdist(kleinify w,kleinify z) = mdist(kleinify w',kleinify z')`,
350 SIMP_TAC[MDIST_KLEINIFY; NORM_EQ_SQUARE; GSYM NORM_POW_2; REAL_POS] THEN
351 CONV_TAC REAL_FIELD);;
353 let NORM_KLEINIFY_MOEBIUS_LT = prove
354 (`!w x. norm w < &1 /\ norm x < &1
355 ==> norm(kleinify(moebius_function (&0) w x)) < &1`,
356 SIMP_TAC[MOEBIUS_FUNCTION_NORM_LT_1; NORM_KLEINIFY_LT; REAL_LT_IMP_NE]);;
358 let MDIST_KLEINIFY_MOEBIUS = prove
359 (`!w x y. norm w < &1 /\ norm x < &1 /\ norm y < &1
360 ==> mdist(kleinify(moebius_function (&0) w x),
361 kleinify(moebius_function (&0) w y)) =
362 mdist(kleinify x,kleinify y)`,
363 REPEAT STRIP_TAC THEN MATCH_MP_TAC MDIST_KLEINIFY_EQ THEN
364 ASM_SIMP_TAC[MOEBIUS_FUNCTION_NORM_LT_1; REAL_LT_IMP_NE] THEN
365 REWRITE_TAC[MOEBIUS_FUNCTION_SIMPLE] THEN
367 `~(Cx(&1) - cnj w * x = Cx(&0)) /\ ~(Cx(&1) - cnj w * y = Cx(&0))`
368 STRIP_ASSUME_TAC THENL
369 [REWRITE_TAC[COMPLEX_SUB_0] THEN CONJ_TAC THEN
370 MATCH_MP_TAC(MESON[REAL_LT_REFL] `norm(x) < norm(y) ==> ~(y = x)`) THEN
371 REWRITE_TAC[COMPLEX_NORM_CX; REAL_ABS_NUM; COMPLEX_NORM_MUL] THEN
372 GEN_REWRITE_TAC RAND_CONV [GSYM REAL_MUL_LID] THEN
373 MATCH_MP_TAC REAL_LT_MUL2 THEN REWRITE_TAC[NORM_POS_LE] THEN
374 ASM_REWRITE_TAC[COMPLEX_NORM_CNJ];
375 ASM_SIMP_TAC[COMPLEX_FIELD
376 `~(Cx(&1) - cnj w * x = Cx(&0)) /\ ~(Cx(&1) - cnj w * y = Cx(&0))
377 ==> (x - w) / (Cx (&1) - cnj w * x) - (y - w) / (Cx (&1) - cnj w * y) =
378 ((Cx(&1) - w * cnj w) * (x - y)) /
379 ((Cx (&1) - cnj w * x) * (Cx (&1) - cnj w * y))`] THEN
380 REWRITE_TAC[COMPLEX_NORM_DIV; COMPLEX_NORM_POW] THEN
381 ASM_SIMP_TAC[COMPLEX_NORM_ZERO; REAL_FIELD
382 `~(y = &0) /\ ~(y' = &0)
383 ==> (&1 - (x / y) pow 2) * (&1 - (x' / y') pow 2) =
384 ((y pow 2 - x pow 2) * (y' pow 2 - x' pow 2)) / (y * y') pow 2`] THEN
385 REWRITE_TAC[REAL_POW_DIV; COMPLEX_NORM_MUL] THEN REWRITE_TAC[real_div] THEN
386 MATCH_MP_TAC(REAL_RING
387 `x * y:real = w * z ==> (x * i) * y = w * z * i`) THEN
388 REWRITE_TAC[GSYM COMPLEX_NORM_MUL] THEN REWRITE_TAC[NORM_POW_2; DOT_2] THEN
389 REWRITE_TAC[GSYM RE_DEF; GSYM IM_DEF; complex_sub; complex_mul; CX_DEF;
390 complex_add; RE; IM; cnj; complex_neg] THEN REAL_ARITH_TAC]);;
392 let COLLINEAR_KLEINIFY_MOEBIUS = prove
393 (`!w x y z. norm w < &1 /\ norm x < &1 /\ norm y < &1 /\ norm z < &1
394 ==> (collinear {kleinify(moebius_function (&0) w x),
395 kleinify(moebius_function (&0) w y),
396 kleinify(moebius_function (&0) w z)} <=>
397 collinear {kleinify x,kleinify y,kleinify z})`,
398 REPEAT STRIP_TAC THEN
399 REWRITE_TAC[COLLINEAR_3_2D; kleinify; GSYM RE_DEF; GSYM IM_DEF] THEN
400 REWRITE_TAC[RE_MUL_CX; IM_MUL_CX] THEN
401 SIMP_TAC[NORM_POS_LE; REAL_POW_LE; REAL_ARITH `&0 <= x ==> ~(&1 + x = &0)`;
403 `~(nx = &0) /\ ~(ny = &0) /\ ~(nz = &0)
404 ==> ((&2 / nz * rz - &2 / nx * rx) * (&2 / ny * iy - &2 / nx * ix) =
405 (&2 / ny * ry - &2 / nx * rx) * (&2 / nz * iz - &2 / nx * ix) <=>
406 (nx * rz - nz * rx) * (nx * iy - ny * ix) =
407 (nx * ry - ny * rx) * (nx * iz - nz * ix))`] THEN
408 REWRITE_TAC[COMPLEX_NORM_DIV; MOEBIUS_FUNCTION_SIMPLE] THEN
409 ONCE_REWRITE_TAC[COMPLEX_DIV_CNJ] THEN
410 REWRITE_TAC[RE_DIV_CX; GSYM CX_POW; IM_DIV_CX] THEN
412 `~(Cx (&1) - cnj w * x = Cx(&0)) /\ ~(Cx (&1) - cnj w * y = Cx(&0)) /\
413 ~(Cx (&1) - cnj w * z = Cx(&0))`
414 STRIP_ASSUME_TAC THENL
415 [REWRITE_TAC[COMPLEX_SUB_0] THEN REPEAT CONJ_TAC THEN
416 MATCH_MP_TAC(MESON[REAL_LT_REFL] `norm x < norm y ==> ~(y = x)`) THEN
417 REWRITE_TAC[COMPLEX_NORM_MUL; COMPLEX_NORM_CNJ; COMPLEX_NORM_CX] THEN
418 ONCE_REWRITE_TAC[REAL_ARITH `abs(&1) = &1 * &1`] THEN
419 MATCH_MP_TAC REAL_LT_MUL2 THEN ASM_REWRITE_TAC[NORM_POS_LE];
421 ASM_SIMP_TAC[COMPLEX_NORM_ZERO; REAL_FIELD
422 `~(nx = &0) /\ ~(ny = &0) /\ ~(nz = &0)
423 ==>(((&1 + (nxw / nx) pow 2) * rz / nz pow 2 -
424 (&1 + (nzw / nz) pow 2) * rx / nx pow 2) *
425 ((&1 + (nxw / nx) pow 2) * iy / ny pow 2 -
426 (&1 + (nyw / ny) pow 2) * ix / nx pow 2) =
427 ((&1 + (nxw / nx) pow 2) * ry / ny pow 2 -
428 (&1 + (nyw / ny) pow 2) * rx / nx pow 2) *
429 ((&1 + (nxw / nx) pow 2) * iz / nz pow 2 -
430 (&1 + (nzw / nz) pow 2) * ix / nx pow 2) <=>
431 ((nx pow 2 + nxw pow 2) * rz - (nz pow 2 + nzw pow 2) * rx) *
432 ((nx pow 2 + nxw pow 2) * iy - (ny pow 2 + nyw pow 2) * ix) =
433 ((nx pow 2 + nxw pow 2) * ry - (ny pow 2 + nyw pow 2) * rx) *
434 ((nx pow 2 + nxw pow 2) * iz - (nz pow 2 + nzw pow 2) * ix))`] THEN
435 REWRITE_TAC[COMPLEX_SQNORM; complex_sub; complex_mul; complex_add;
436 complex_neg; cnj; CX_DEF; RE; IM] THEN
437 ONCE_REWRITE_TAC[GSYM REAL_SUB_0] THEN MATCH_MP_TAC(REAL_RING
438 `!a b. a * lhs = b * rhs /\ ~(a = &0) /\ ~(b = &0)
439 ==> (lhs = &0 <=> rhs = &0)`) THEN
440 EXISTS_TAC `Re x pow 2 + Im x pow 2 + &1` THEN
441 EXISTS_TAC `--(Re w pow 2 + Im w pow 2 - &1) pow 3 *
442 ((&1 - Re(x) pow 2 - Im(x) pow 2) *
443 (&1 - Re(w) pow 2 - Im(w) pow 2) +
444 &2 * (Re w - Re x) pow 2 + &2 * (Im w - Im x) pow 2)` THEN
445 REWRITE_TAC[REAL_ENTIRE; DE_MORGAN_THM; REAL_POW_EQ_0; ARITH_EQ] THEN
446 REPEAT CONJ_TAC THENL
448 MATCH_MP_TAC(REAL_ARITH `&0 <= x + y ==> ~(x + y + &1 = &0)`) THEN
449 ASM_SIMP_TAC[GSYM COMPLEX_SQNORM; REAL_LE_POW_2];
450 MATCH_MP_TAC(REAL_ARITH `x + y < &1 ==> ~(--(x + y - &1) = &0)`) THEN
451 ASM_SIMP_TAC[GSYM COMPLEX_SQNORM; REAL_POW_1_LT; NORM_POS_LE; ARITH];
452 MATCH_MP_TAC(REAL_ARITH `&0 < x /\ &0 <= y ==> ~(x + y = &0)`) THEN
453 SIMP_TAC[REAL_LE_ADD; REAL_LE_MUL; REAL_POS; REAL_LE_POW_2] THEN
454 MATCH_MP_TAC REAL_LT_MUL THEN
455 ASM_REWRITE_TAC[REAL_ARITH `&0 < &1 - x - y <=> x + y < &1`] THEN
456 ASM_SIMP_TAC[GSYM COMPLEX_SQNORM; REAL_POW_1_LT; NORM_POS_LE; ARITH]]);;
458 let BETWEEN_KLEINIFY_MOEBIUS = prove
459 (`!w x y z. norm w < &1 /\ norm x < &1 /\ norm y < &1 /\ norm z < &1
460 ==> (between (kleinify(moebius_function (&0) w x))
461 (kleinify(moebius_function (&0) w y),
462 kleinify(moebius_function (&0) w z)) <=>
463 between (kleinify x) (kleinify y,kleinify z))`,
464 SIMP_TAC[BETWEEN_COLLINEAR_MDIST_EQ; NORM_KLEINIFY_MOEBIUS_LT;
465 NORM_KLEINIFY_LT; REAL_LT_IMP_NE;
466 COLLINEAR_KLEINIFY_MOEBIUS; MDIST_KLEINIFY_MOEBIUS]);;
468 let hyperbolic_isometry = new_definition
469 `hyperbolic_isometry (f:real^2->real^2) <=>
470 (!x. norm x < &1 ==> norm(f x) < &1) /\
471 (!x y. norm x < &1 /\ norm y < &1 ==> mdist(f x,f y) = mdist(x,y)) /\
472 (!x y z. norm x < &1 /\ norm y < &1 /\ norm z < &1
473 ==> (between (f x) (f y,f z) <=> between x (y,z)))`;;
475 let HYPERBOLIC_TRANSLATION = prove
477 ==> ?f:real^2->real^2 g:real^2->real^2.
478 hyperbolic_isometry f /\ hyperbolic_isometry g /\
479 f(w) = vec 0 /\ g(vec 0) = w /\
480 (!x. norm x < &1 ==> f(g x) = x) /\
481 (!x. norm x < &1 ==> g(f x) = x)`,
482 REPEAT STRIP_TAC THEN SIMP_TAC[hyperbolic_isometry] THEN MAP_EVERY EXISTS_TAC
483 [`\x. kleinify(moebius_function(&0) (poincarify w) (poincarify x))`;
484 `\x. kleinify(moebius_function(&0) (--(poincarify w)) (poincarify x))`] THEN
485 ASM_SIMP_TAC[NORM_KLEINIFY_MOEBIUS_LT; NORM_POINCARIFY_LT;
486 MDIST_KLEINIFY_MOEBIUS; KLEINIFY_POINCARIFY; VECTOR_NEG_NEG;
487 BETWEEN_KLEINIFY_MOEBIUS; NORM_NEG; MOEBIUS_FUNCTION_COMPOSE;
488 POINCARIFY_KLEINIFY; MOEBIUS_FUNCTION_NORM_LT_1] THEN
489 ASM_SIMP_TAC[MOEBIUS_FUNCTION_SIMPLE; COMPLEX_SUB_REFL; complex_div;
490 COMPLEX_VEC_0; KLEINIFY_0; POINCARIFY_0; COMPLEX_MUL_LZERO;
491 COMPLEX_MUL_RZERO; COMPLEX_SUB_LZERO; COMPLEX_NEG_NEG;
492 COMPLEX_SUB_RZERO; COMPLEX_INV_1; COMPLEX_MUL_RID;
493 KLEINIFY_POINCARIFY]);;
495 (* ------------------------------------------------------------------------- *)
497 (* ------------------------------------------------------------------------- *)
501 (`?x:real^2. norm x < &1`,
502 EXISTS_TAC `vec 0:real^2` THEN NORM_ARITH_TAC) in
503 new_type_definition "plane" ("mk_plane","dest_plane") th;;
505 let pbetween = new_definition
506 `pbetween y (x,z) <=> between (dest_plane y) (dest_plane x,dest_plane z)`;;
508 let pdist = new_definition
509 `pdist(x,y) = mdist(dest_plane x,dest_plane y)`;;
511 let DEST_PLANE_NORM_LT = prove
512 (`!x. norm(dest_plane x) < &1`,
513 MESON_TAC[plane_tybij]);;
515 let DEST_PLANE_EQ = prove
516 (`!x y. dest_plane x = dest_plane y <=> x = y`,
517 MESON_TAC[plane_tybij]);;
519 let FORALL_DEST_PLANE = prove
520 (`!P. (!x. P(dest_plane x)) <=> (!x. norm x < &1 ==> P x)`,
521 MESON_TAC[plane_tybij]);;
523 let EXISTS_DEST_PLANE = prove
524 (`!P. (?x. P(dest_plane x)) <=> (?x. norm x < &1 /\ P x)`,
525 MESON_TAC[plane_tybij]);;
527 (* ------------------------------------------------------------------------- *)
528 (* Axiom 1 (reflexivity for equidistance). *)
529 (* ------------------------------------------------------------------------- *)
531 let TARSKI_AXIOM_1_NONEUCLIDEAN = prove
532 (`!a b. pdist(a,b) = pdist(b,a)`,
533 REWRITE_TAC[pdist; MDIST_SYM]);;
535 (* ------------------------------------------------------------------------- *)
536 (* Axiom 2 (transitivity for equidistance). *)
537 (* ------------------------------------------------------------------------- *)
539 let TARSKI_AXIOM_2_NONEUCLIDEAN = prove
541 pdist(a,b) = pdist(p,q) /\ pdist(a,b) = pdist(r,s)
542 ==> pdist(p,q) = pdist(r,s)`,
545 (* ------------------------------------------------------------------------- *)
546 (* Axiom 3 (identity for equidistance). *)
547 (* ------------------------------------------------------------------------- *)
549 let TARSKI_AXIOM_3_NONEUCLIDEAN = prove
550 (`!a b c. pdist(a,b) = pdist(c,c) ==> a = b`,
551 SIMP_TAC[FORALL_DEST_PLANE; pdist; MDIST_REFL; MDIST_EQ_0; DEST_PLANE_EQ]);;
553 (* ------------------------------------------------------------------------- *)
554 (* Axiom 4 (segment construction). *)
555 (* ------------------------------------------------------------------------- *)
557 let TARSKI_AXIOM_4_NONEUCLIDEAN = prove
558 (`!a q b c. ?x. pbetween a (q,x) /\ pdist(a,x) = pdist(b,c)`,
559 REWRITE_TAC[pbetween; pdist; FORALL_DEST_PLANE; EXISTS_DEST_PLANE] THEN
560 REWRITE_TAC[RIGHT_IMP_FORALL_THM; IMP_IMP; GSYM CONJ_ASSOC] THEN
561 REPEAT GEN_TAC THEN DISCH_TAC THEN
562 SUBGOAL_THEN `?d:real^2. norm d < &1 /\ mdist(b:real^2,c) = mdist(vec 0,d)`
563 STRIP_ASSUME_TAC THENL
564 [MP_TAC(SPEC `b:real^2` HYPERBOLIC_TRANSLATION) THEN
565 ASM_REWRITE_TAC[hyperbolic_isometry] THEN ASM_MESON_TAC[];
566 ASM_REWRITE_TAC[]] THEN
568 `norm(a:real^2) < &1 /\ norm(q:real^2) < &1 /\ norm(d:real^2) < &1`
569 MP_TAC THENL [ASM_REWRITE_TAC[]; REPEAT(POP_ASSUM(K ALL_TAC))] THEN
570 MAP_EVERY (fun t -> SPEC_TAC(t,t)) [`d:real^2`; `q:real^2`; `a:real^2`] THEN
571 MATCH_MP_TAC(MESON[] `P(vec 0) /\ (P(vec 0) ==> !x. P x) ==> !x. P x`) THEN
572 REWRITE_TAC[NORM_0; REAL_LT_01] THEN CONJ_TAC THENL
573 [MP_TAC(ISPEC `vec 0:real^2` TARSKI_AXIOM_4_EUCLIDEAN) THEN
574 MESON_TAC[DIST_0; MDIST_EQ_ORIGIN];
575 DISCH_THEN(LABEL_TAC "*") THEN REPEAT STRIP_TAC THEN
576 MP_TAC(ISPEC `a:real^2` HYPERBOLIC_TRANSLATION) THEN
577 ASM_REWRITE_TAC[hyperbolic_isometry; LEFT_IMP_EXISTS_THM] THEN
578 MAP_EVERY X_GEN_TAC [`f:real^2->real^2`; `g:real^2->real^2`] THEN
580 REMOVE_THEN "*" (MP_TAC o SPECL [`(f:real^2->real^2) q`; `d:real^2`]) THEN
582 DISCH_THEN(X_CHOOSE_THEN `x:real^2` STRIP_ASSUME_TAC) THEN
583 EXISTS_TAC `(g:real^2->real^2) x` THEN ASM_MESON_TAC[]]);;
585 (* ------------------------------------------------------------------------- *)
586 (* Axiom 5 (five-segments axiom). *)
587 (* ------------------------------------------------------------------------- *)
589 let TARSKI_AXIOM_5_NONEUCLIDEAN = prove
590 (`!a b c x a' b' c' x'.
592 pdist(a,b) = pdist(a',b') /\
593 pdist(a,c) = pdist(a',c') /\
594 pdist(b,c) = pdist(b',c') /\
595 pbetween b (a,x) /\ pbetween b' (a',x') /\ pdist(b,x) = pdist(b',x')
596 ==> pdist(c,x) = pdist(c',x')`,
597 REWRITE_TAC[FORALL_DEST_PLANE; pdist; pbetween; GSYM DEST_PLANE_EQ] THEN
598 REPEAT STRIP_TAC THEN MP_TAC(ISPEC `b':real^2` HYPERBOLIC_TRANSLATION) THEN
599 MP_TAC(ISPEC `b:real^2` HYPERBOLIC_TRANSLATION) THEN
600 ASM_REWRITE_TAC[RIGHT_IMP_FORALL_THM; LEFT_IMP_EXISTS_THM] THEN
601 REWRITE_TAC[hyperbolic_isometry] THEN MAP_EVERY X_GEN_TAC
602 [`f:real^2->real^2`; `f':real^2->real^2`; `g:real^2->real^2`;
603 `g':real^2->real^2`] THEN REPEAT STRIP_TAC THEN
604 MP_TAC(ISPECL [`(f:real^2->real^2) x`; `(f:real^2->real^2) c`;
605 `(g:real^2->real^2) x'`; `(g:real^2->real^2) c'`]
606 MDIST_CONGRUENT_TRIPLES_0) THEN
607 ANTS_TAC THENL [ASM_MESON_TAC[]; ALL_TAC] THEN
608 MATCH_MP_TAC(TAUT `(p ==> r) /\ q ==> (p <=> q) ==> r`) THEN
609 CONJ_TAC THENL [ASM_MESON_TAC[MDIST_SYM]; ALL_TAC] THEN
610 MP_TAC(ISPECL [`(f:real^2->real^2) a`; `(f:real^2->real^2) c`;
611 `(g:real^2->real^2) a'`; `(g:real^2->real^2) c'`]
612 MDIST_CONGRUENT_TRIPLES_0) THEN
613 ANTS_TAC THENL [ASM_MESON_TAC[]; ALL_TAC] THEN
614 MATCH_MP_TAC(TAUT `p /\ (q ==> r) ==> (p <=> q) ==> r`) THEN CONJ_TAC THENL
615 [ASM_SIMP_TAC[GSYM MDIST_CONGRUENT_TRIPLES_0] THEN CONJ_TAC THEN
616 GEN_REWRITE_TAC (LAND_CONV o ONCE_DEPTH_CONV)
617 [SYM(ASSUME `(f:complex->complex) b = vec 0`)] THEN
618 GEN_REWRITE_TAC (RAND_CONV o ONCE_DEPTH_CONV)
619 [SYM(ASSUME `(g:complex->complex) b' = vec 0`)] THEN
620 ASM_SIMP_TAC[] THEN ASM_MESON_TAC[MDIST_SYM];
621 STRIP_TAC THEN MP_TAC(ISPECL
622 [`(f:real^2->real^2) a`; `(f:real^2->real^2) b`; `(f:real^2->real^2) c`;
623 `(f:real^2->real^2) x`;`(g:real^2->real^2) a'`; `(g:real^2->real^2) b'`;
624 `(g:real^2->real^2) c'`; `(g:real^2->real^2) x'`]
625 TARSKI_AXIOM_5_EUCLIDEAN) THEN
627 `mdist((f:real^2->real^2) b,f x) = mdist((g:real^2->real^2) b',g x')`
630 ASM_REWRITE_TAC[] THEN ASM_SIMP_TAC[MDIST_EQ_ORIGIN] THEN DISCH_TAC] THEN
631 ASM_MESON_TAC[DIST_SYM; DIST_0]]);;
633 (* ------------------------------------------------------------------------- *)
634 (* Axiom 6 (identity for between-ness). *)
635 (* ------------------------------------------------------------------------- *)
637 let TARSKI_AXIOM_6_NONEUCLIDEAN = prove
638 (`!a b. pbetween b (a,a) ==> a = b`,
639 REWRITE_TAC[pbetween; FORALL_DEST_PLANE; GSYM DEST_PLANE_EQ] THEN
640 MESON_TAC[TARSKI_AXIOM_6_EUCLIDEAN]);;
642 (* ------------------------------------------------------------------------- *)
643 (* Axiom 7 (Pasch's axiom). *)
644 (* ------------------------------------------------------------------------- *)
646 let TARSKI_AXIOM_7_NONEUCLIDEAN = prove
648 pbetween p (a,c) /\ pbetween q (b,c)
649 ==> ?x. pbetween x (p,b) /\ pbetween x (q,a)`,
650 REWRITE_TAC[pbetween; FORALL_DEST_PLANE; EXISTS_DEST_PLANE] THEN
651 MESON_TAC[BETWEEN_NORM_LT; TARSKI_AXIOM_7_EUCLIDEAN]);;
653 (* ------------------------------------------------------------------------- *)
654 (* Axiom 8 (lower 2-dimensional axiom). *)
655 (* ------------------------------------------------------------------------- *)
657 let TARSKI_AXIOM_8_NONEUCLIDEAN = prove
658 (`?a b c. ~pbetween b (a,c) /\ ~pbetween c (b,a) /\ ~pbetween a (c,b)`,
659 REWRITE_TAC[pbetween; EXISTS_DEST_PLANE; NORM_LT_SQUARE; NORM_POW_2] THEN
660 MAP_EVERY (fun t -> EXISTS_TAC t THEN
661 SIMP_TAC[DOT_LMUL; DOT_RMUL; DOT_BASIS_BASIS; DIMINDEX_2; ARITH] THEN
662 REWRITE_TAC[DOT_LZERO] THEN CONV_TAC REAL_RAT_REDUCE_CONV)
663 [`vec 0:real^2`; `(&1 / &2) % basis 1:real^2`;
664 `(&1 / &2) % basis 2:real^2`] THEN
665 REPEAT CONJ_TAC THEN DISCH_THEN(MP_TAC o MATCH_MP BETWEEN_IMP_COLLINEAR) THEN
666 SIMP_TAC[COLLINEAR_3_2D; VECTOR_MUL_COMPONENT; VEC_COMPONENT; ARITH;
667 BASIS_COMPONENT; DIMINDEX_2] THEN CONV_TAC REAL_RAT_REDUCE_CONV);;
669 (* ------------------------------------------------------------------------- *)
670 (* Axiom 9 (upper 2-dimensional axiom). *)
671 (* ------------------------------------------------------------------------- *)
673 let TARSKI_AXIOM_9_NONEUCLIDEAN = prove
676 pdist(a,p) = pdist(a,q) /\ pdist(b,p) = pdist(b,q) /\
677 pdist(c,p) = pdist(c,q)
678 ==> pbetween b (a,c) \/ pbetween c (b,a) \/ pbetween a (c,b)`,
679 REWRITE_TAC[pdist; pbetween; FORALL_DEST_PLANE; GSYM DEST_PLANE_EQ] THEN
680 REWRITE_TAC[RIGHT_IMP_FORALL_THM; IMP_IMP; GSYM CONJ_ASSOC] THEN
681 REPEAT STRIP_TAC THEN
682 MP_TAC(ISPECL [`p:real^2`; `q:real^2`] HYPERBOLIC_MIDPOINT) THEN
683 ASM_REWRITE_TAC[LEFT_IMP_EXISTS_THM] THEN X_GEN_TAC `x:real^2` THEN
684 STRIP_TAC THEN MP_TAC(ISPEC `x:real^2` HYPERBOLIC_TRANSLATION) THEN
685 SUBGOAL_THEN `norm(x:real^2) < &1` ASSUME_TAC THENL
686 [ASM_MESON_TAC[BETWEEN_NORM_LT]; ONCE_REWRITE_TAC[BETWEEN_SYM]] THEN
687 ASM_REWRITE_TAC[LEFT_IMP_EXISTS_THM; hyperbolic_isometry] THEN
688 REWRITE_TAC[GSYM COLLINEAR_BETWEEN_CASES] THEN REPEAT STRIP_TAC THEN
689 SUBGOAL_THEN `collinear{(f:real^2->real^2) b,f c,f a}` MP_TAC THENL
690 [ALL_TAC; ASM_SIMP_TAC[COLLINEAR_BETWEEN_CASES]] THEN
691 SUBGOAL_THEN `mdist(f a,f p) = mdist(f a,f q) /\
692 mdist(f b,f p) = mdist(f b,f q) /\
693 mdist(f c,f p) = mdist(f c,f q) /\
694 ~((f:real^2->real^2) q = f p)`
695 MP_TAC THENL [ASM_MESON_TAC[]; ALL_TAC] THEN
696 SUBGOAL_THEN `(f:real^2->real^2) q = --(f p)` SUBST1_TAC THENL
697 [SUBGOAL_THEN `between ((f:real^2->real^2) x) (f p,f q) /\
698 mdist(f x,f p) = mdist(f x,f q)`
699 MP_TAC THENL [ASM_MESON_TAC[]; ALL_TAC] THEN
700 ASM_REWRITE_TAC[] THEN ASM_SIMP_TAC[MDIST_EQ_ORIGIN] THEN
701 REWRITE_TAC[GSYM MIDPOINT_BETWEEN; midpoint; NORM_ARITH
702 `norm(a:real^N) = norm b <=> dist(a,vec 0) = dist(vec 0,b)`] THEN
704 REWRITE_TAC[mdist] THEN ASM_SIMP_TAC[NORM_NEG; real_div; REAL_INV_MUL] THEN
705 ASM_SIMP_TAC[REAL_SUB_LT; ABS_SQUARE_LT_1; REAL_ABS_NORM; REAL_FIELD
707 ==> (a * inv x * inv y - &1 = b * inv x * inv y - &1 <=> a = b)`] THEN
708 ONCE_REWRITE_TAC[VECTOR_ARITH `--x:real^N = x <=> x = vec 0`] THEN
709 REWRITE_TAC[COLLINEAR_3_2D; VECTOR_SUB_COMPONENT; DOT_2; GSYM DOT_EQ_0;
710 VECTOR_NEG_COMPONENT] THEN CONV_TAC REAL_RING]);;
712 (* ------------------------------------------------------------------------- *)
713 (* Axiom 10 (Euclidean axiom). *)
714 (* ------------------------------------------------------------------------- *)
716 let NOT_TARSKI_AXIOM_10_NONEUCLIDEAN = prove
718 pbetween d (a,t) /\ pbetween d (b,c) /\ ~(a = d)
719 ==> ?x y. pbetween b (a,x) /\ pbetween c (a,y) /\ pbetween t (x,y))`,
720 REWRITE_TAC[pbetween; FORALL_DEST_PLANE; EXISTS_DEST_PLANE;
721 GSYM DEST_PLANE_EQ; RIGHT_IMP_FORALL_THM; IMP_IMP] THEN
722 DISCH_THEN(MP_TAC o SPECL
723 [`vec 0:real^2`; `&1 / &2 % basis 1:real^2`; `&1 / &2 % basis 2:real^2`;
724 `&1 / &4 % basis 1 + &1 / &4 % basis 2:real^2`;
725 `&3 / &5 % basis 1 + &3 / &5 % basis 2:real^2`]) THEN
726 REWRITE_TAC[NOT_IMP; CONJ_ASSOC] THEN CONJ_TAC THENL
728 REWRITE_TAC[NOT_EXISTS_THM; TAUT `~(p /\ q) <=> p ==> ~q`] THEN
729 REWRITE_TAC[IMP_CONJ] THEN REPEAT(GEN_TAC THEN DISCH_TAC) THEN
730 REWRITE_TAC[IMP_IMP] THEN
731 DISCH_THEN(CONJUNCTS_THEN (MP_TAC o MATCH_MP BETWEEN_IMP_COLLINEAR)) THEN
732 SIMP_TAC[COLLINEAR_3_2D; BASIS_COMPONENT; DIMINDEX_2; ARITH; VEC_COMPONENT;
733 VECTOR_MUL_COMPONENT] THEN CONV_TAC REAL_RAT_REDUCE_CONV THEN
734 REWRITE_TAC[REAL_SUB_LZERO; REAL_MUL_LZERO; REAL_MUL_RZERO; REAL_SUB_RZERO;
735 REAL_ARITH `&0 = &1 / &2 * x <=> x = &0`] THEN
736 REWRITE_TAC[REAL_ENTIRE] THEN CONV_TAC REAL_RAT_REDUCE_CONV THEN
737 MP_TAC(ISPECL [`x:real^2`; `1`] COMPONENT_LE_NORM) THEN
738 MP_TAC(ISPECL [`y:real^2`; `2`] COMPONENT_LE_NORM) THEN
739 SIMP_TAC[DIMINDEX_2; ARITH; BETWEEN_IN_SEGMENT; IN_SEGMENT] THEN
740 REPEAT STRIP_TAC THEN SUBGOAL_THEN
741 `norm(&3 / &5 % basis 1 + &3 / &5 % basis 2:real^2) pow 2 <= &1 / &2`
743 [SUBGOAL_THEN `(&3 / &5 % basis 1 + &3 / &5 % basis 2:real^2)$2 =
744 (&3 / &5 % basis 1 + &3 / &5 % basis 2:real^2)$1`
746 [SIMP_TAC[CART_EQ; DIMINDEX_2; FORALL_2; ARITH; BASIS_COMPONENT;
747 VECTOR_ADD_COMPONENT; VECTOR_MUL_COMPONENT; VEC_COMPONENT] THEN
749 ASM_REWRITE_TAC[]] THEN
750 REWRITE_TAC[NORM_POW_2; DOT_LADD; DOT_RADD; DOT_LMUL; DOT_RMUL] THEN
751 ASM_SIMP_TAC[DIMINDEX_2; FORALL_2; DOT_2; VECTOR_ADD_COMPONENT; ARITH;
752 VECTOR_MUL_COMPONENT; BASIS_COMPONENT; DIMINDEX_2] THEN
753 DISCH_THEN(MP_TAC o MATCH_MP (REAL_ARITH
754 `a * &0 + y = x + b * &0 ==> abs x + abs y <= (&1 - u) * &1 + u * &1
755 ==> abs x <= abs(&1 / &2) /\ abs y <= abs(&1 / &2)`)) THEN
757 [REWRITE_TAC[REAL_ABS_MUL] THEN MATCH_MP_TAC REAL_LE_ADD2 THEN
758 CONJ_TAC THEN MATCH_MP_TAC REAL_LE_MUL2 THEN ASM_REAL_ARITH_TAC;
759 REWRITE_TAC[REAL_LE_SQUARE_ABS] THEN REAL_ARITH_TAC];
761 SIMP_TAC[NORM_LT_SQUARE; NORM_POW_2; DOT_LADD; DOT_RADD; DOT_LZERO;
762 DOT_LMUL; DOT_RMUL; DOT_BASIS_BASIS; DIMINDEX_2; ARITH] THEN
763 CONV_TAC REAL_RAT_REDUCE_CONV THEN
764 REWRITE_TAC[BETWEEN_IN_SEGMENT; IN_SEGMENT] THEN REPEAT CONJ_TAC THENL
765 [EXISTS_TAC `&5 / &12`; EXISTS_TAC `&1 / &2`; ALL_TAC] THEN
766 SIMP_TAC[CART_EQ; DIMINDEX_2; FORALL_2; ARITH; BASIS_COMPONENT;
767 VECTOR_ADD_COMPONENT; VECTOR_MUL_COMPONENT; VEC_COMPONENT] THEN
768 CONV_TAC REAL_RAT_REDUCE_CONV);;
770 (* ------------------------------------------------------------------------- *)
771 (* Axiom 11 (Continuity). *)
772 (* ------------------------------------------------------------------------- *)
774 let TARSKI_AXIOM_11_NONEUCLIDEAN = prove
775 (`!X Y. (?a. !x y. x IN X /\ y IN Y ==> pbetween x (a,y))
776 ==> (?b. !x y. x IN X /\ y IN Y ==> pbetween b (x,y))`,
778 ASM_CASES_TAC `X:plane->bool = {}` THEN ASM_REWRITE_TAC[NOT_IN_EMPTY] THEN
779 ASM_CASES_TAC `Y:plane->bool = {}` THEN ASM_REWRITE_TAC[NOT_IN_EMPTY] THEN
780 REWRITE_TAC[pbetween; EXISTS_DEST_PLANE] THEN
781 DISCH_THEN(X_CHOOSE_THEN `a:real^2` STRIP_ASSUME_TAC) THEN
782 MP_TAC(ISPECL [`IMAGE dest_plane X`; `IMAGE dest_plane Y`]
783 TARSKI_AXIOM_11_EUCLIDEAN) THEN REWRITE_TAC[IN_IMAGE] THEN
784 ANTS_TAC THENL [ASM SET_TAC[]; MATCH_MP_TAC MONO_EXISTS] THEN
785 ASM_MESON_TAC[MEMBER_NOT_EMPTY; DEST_PLANE_NORM_LT; BETWEEN_NORM_LT]);;