:: Special Polygons
:: by Czes\law Byli\'nski and Yatsuka Nakamura
::
:: Received January 30, 1995
:: Copyright (c) 1995-2021 Association of Mizar Users


theorem :: SPPOL_2:1
for r1, r2, r19, r29 being Real st |[r1,r2]| = |[r19,r29]| holds
( r1 = r19 & r2 = r29 ) by FINSEQ_1:77;

theorem Th2: :: SPPOL_2:2
for f being FinSequence of (TOP-REAL 2)
for i, j being Nat st i + j = len f holds
LSeg (f,i) = LSeg ((Rev f),j)
proof end;

theorem Th3: :: SPPOL_2:3
for f being FinSequence of (TOP-REAL 2)
for i, n being Nat st i + 1 <= len (f | n) holds
LSeg ((f | n),i) = LSeg (f,i)
proof end;

theorem Th4: :: SPPOL_2:4
for f being FinSequence of (TOP-REAL 2)
for i, n being Nat st n <= len f & 1 <= i holds
LSeg ((f /^ n),i) = LSeg (f,(n + i))
proof end;

theorem Th5: :: SPPOL_2:5
for f being FinSequence of (TOP-REAL 2)
for i, n being Nat st 1 <= i & i + 1 <= (len f) - n holds
LSeg ((f /^ n),i) = LSeg (f,(n + i))
proof end;

theorem Th6: :: SPPOL_2:6
for f, g being FinSequence of (TOP-REAL 2)
for i being Nat st i + 1 <= len f holds
LSeg ((f ^ g),i) = LSeg (f,i)
proof end;

theorem Th7: :: SPPOL_2:7
for f, g being FinSequence of (TOP-REAL 2)
for i being Nat st 1 <= i holds
LSeg ((f ^ g),((len f) + i)) = LSeg (g,i)
proof end;

theorem Th8: :: SPPOL_2:8
for f, g being FinSequence of (TOP-REAL 2) st not f is empty & not g is empty holds
LSeg ((f ^ g),(len f)) = LSeg ((f /. (len f)),(g /. 1))
proof end;

theorem Th9: :: SPPOL_2:9
for f being FinSequence of (TOP-REAL 2)
for p being Point of (TOP-REAL 2)
for i being Nat st i + 1 <= len (f -: p) holds
LSeg ((f -: p),i) = LSeg (f,i)
proof end;

theorem Th10: :: SPPOL_2:10
for f being FinSequence of (TOP-REAL 2)
for p being Point of (TOP-REAL 2)
for i being Nat st p in rng f holds
LSeg ((f :- p),(i + 1)) = LSeg (f,(i + (p .. f)))
proof end;

theorem Th11: :: SPPOL_2:11
L~ (<*> the carrier of (TOP-REAL 2)) = {} by TOPREAL1:22;

theorem Th12: :: SPPOL_2:12
for p being Point of (TOP-REAL 2) holds L~ <*p*> = {} by FINSEQ_1:39, TOPREAL1:22;

theorem Th13: :: SPPOL_2:13
for f being FinSequence of (TOP-REAL 2)
for p being Point of (TOP-REAL 2) st p in L~ f holds
ex i being Nat st
( 1 <= i & i + 1 <= len f & p in LSeg (f,i) )
proof end;

theorem Th14: :: SPPOL_2:14
for f being FinSequence of (TOP-REAL 2)
for p being Point of (TOP-REAL 2) st p in L~ f holds
ex i being Nat st
( 1 <= i & i + 1 <= len f & p in LSeg ((f /. i),(f /. (i + 1))) )
proof end;

theorem Th15: :: SPPOL_2:15
for f being FinSequence of (TOP-REAL 2)
for p being Point of (TOP-REAL 2)
for i being Nat st 1 <= i & i + 1 <= len f & p in LSeg ((f /. i),(f /. (i + 1))) holds
p in L~ f
proof end;

theorem :: SPPOL_2:16
for f being FinSequence of (TOP-REAL 2)
for i being Nat st 1 <= i & i + 1 <= len f holds
LSeg ((f /. i),(f /. (i + 1))) c= L~ f
proof end;

theorem :: SPPOL_2:17
for f being FinSequence of (TOP-REAL 2)
for p being Point of (TOP-REAL 2)
for i being Nat st p in LSeg (f,i) holds
p in L~ f
proof end;

theorem Th18: :: SPPOL_2:18
for f being FinSequence of (TOP-REAL 2) st len f >= 2 holds
rng f c= L~ f
proof end;

theorem Th19: :: SPPOL_2:19
for f being FinSequence of (TOP-REAL 2)
for p being Point of (TOP-REAL 2) st not f is empty holds
L~ (f ^ <*p*>) = (L~ f) \/ (LSeg ((f /. (len f)),p))
proof end;

theorem Th20: :: SPPOL_2:20
for f being FinSequence of (TOP-REAL 2)
for p being Point of (TOP-REAL 2) st not f is empty holds
L~ (<*p*> ^ f) = (LSeg (p,(f /. 1))) \/ (L~ f)
proof end;

theorem Th21: :: SPPOL_2:21
for p, q being Point of (TOP-REAL 2) holds L~ <*p,q*> = LSeg (p,q)
proof end;

theorem Th22: :: SPPOL_2:22
for f being FinSequence of (TOP-REAL 2) holds L~ f = L~ (Rev f)
proof end;

theorem Th23: :: SPPOL_2:23
for f1, f2 being FinSequence of (TOP-REAL 2) st not f1 is empty & not f2 is empty holds
L~ (f1 ^ f2) = ((L~ f1) \/ (LSeg ((f1 /. (len f1)),(f2 /. 1)))) \/ (L~ f2)
proof end;

Lm1: for f being FinSequence of (TOP-REAL 2)
for n being Nat holds L~ (f | n) c= L~ f
proof end;

theorem Th24: :: SPPOL_2:24
for f being FinSequence of (TOP-REAL 2)
for q being Point of (TOP-REAL 2) st q in rng f holds
L~ f = (L~ (f -: q)) \/ (L~ (f :- q))
proof end;

theorem Th25: :: SPPOL_2:25
for f being FinSequence of (TOP-REAL 2)
for p being Point of (TOP-REAL 2)
for n being Nat st p in LSeg (f,n) holds
L~ f = L~ (Ins (f,n,p))
proof end;

registration
cluster V4() V7( NAT ) V8( the carrier of (TOP-REAL 2)) Function-like V38() FinSequence-like FinSubsequence-like being_S-Seq for FinSequence of the carrier of (TOP-REAL 2);
existence
ex b1 being FinSequence of (TOP-REAL 2) st b1 is being_S-Seq
proof end;
cluster being_S-Seq -> non trivial one-to-one special unfolded s.n.c. for FinSequence of the carrier of (TOP-REAL 2);
coherence
for b1 being FinSequence of (TOP-REAL 2) st b1 is being_S-Seq holds
( b1 is one-to-one & b1 is unfolded & b1 is s.n.c. & b1 is special & not b1 is trivial ) by NAT_D:60;
cluster non trivial one-to-one special unfolded s.n.c. -> being_S-Seq for FinSequence of the carrier of (TOP-REAL 2);
coherence
for b1 being FinSequence of (TOP-REAL 2) st b1 is one-to-one & b1 is unfolded & b1 is s.n.c. & b1 is special & not b1 is trivial holds
b1 is being_S-Seq by NAT_D:60;
cluster being_S-Seq -> non empty for FinSequence of the carrier of (TOP-REAL 2);
coherence
for b1 being FinSequence of (TOP-REAL 2) st b1 is being_S-Seq holds
not b1 is empty ;
end;

registration
cluster V4() V7( NAT ) V8( the carrier of (TOP-REAL 2)) non trivial Function-like one-to-one V38() FinSequence-like FinSubsequence-like special unfolded s.n.c. for FinSequence of the carrier of (TOP-REAL 2);
existence
ex b1 being FinSequence of (TOP-REAL 2) st
( b1 is one-to-one & b1 is unfolded & b1 is s.n.c. & b1 is special & not b1 is trivial )
proof end;
end;

theorem Th26: :: SPPOL_2:26
for f being FinSequence of (TOP-REAL 2) st len f <= 2 holds
f is unfolded
proof end;

Lm2: for p, q being Point of (TOP-REAL 2) holds <*p,q*> is unfolded
proof end;

Lm3: for f being FinSequence of (TOP-REAL 2)
for n being Nat st f is unfolded holds
f | n is unfolded
proof end;

Lm4: for f being FinSequence of (TOP-REAL 2)
for n being Nat st f is unfolded holds
f /^ n is unfolded
proof end;

registration
let f be unfolded FinSequence of (TOP-REAL 2);
let n be Nat;
cluster f | n -> unfolded for FinSequence of (TOP-REAL 2);
coherence
for b1 being FinSequence of (TOP-REAL 2) st b1 = f | n holds
b1 is unfolded by Lm3;
cluster f /^ n -> unfolded for FinSequence of (TOP-REAL 2);
coherence
for b1 being FinSequence of (TOP-REAL 2) st b1 = f /^ n holds
b1 is unfolded by Lm4;
end;

theorem Th27: :: SPPOL_2:27
for f being FinSequence of (TOP-REAL 2)
for p being Point of (TOP-REAL 2) st p in rng f & f is unfolded holds
f :- p is unfolded
proof end;

Lm5: for f being FinSequence of (TOP-REAL 2)
for p being Point of (TOP-REAL 2) st f is unfolded holds
f -: p is unfolded
proof end;

registration
let f be unfolded FinSequence of (TOP-REAL 2);
let p be Point of (TOP-REAL 2);
cluster f -: p -> unfolded ;
coherence
f -: p is unfolded by Lm5;
end;

theorem Th28: :: SPPOL_2:28
for f being FinSequence of (TOP-REAL 2) st f is unfolded holds
Rev f is unfolded
proof end;

theorem Th29: :: SPPOL_2:29
for g being FinSequence of (TOP-REAL 2)
for p being Point of (TOP-REAL 2) st g is unfolded & (LSeg (p,(g /. 1))) /\ (LSeg (g,1)) = {(g /. 1)} holds
<*p*> ^ g is unfolded
proof end;

theorem Th30: :: SPPOL_2:30
for f being FinSequence of (TOP-REAL 2)
for p being Point of (TOP-REAL 2)
for k being Nat st f is unfolded & k + 1 = len f & (LSeg (f,k)) /\ (LSeg ((f /. (len f)),p)) = {(f /. (len f))} holds
f ^ <*p*> is unfolded
proof end;

theorem Th31: :: SPPOL_2:31
for f, g being FinSequence of (TOP-REAL 2)
for k being Nat st f is unfolded & g is unfolded & k + 1 = len f & (LSeg (f,k)) /\ (LSeg ((f /. (len f)),(g /. 1))) = {(f /. (len f))} & (LSeg ((f /. (len f)),(g /. 1))) /\ (LSeg (g,1)) = {(g /. 1)} holds
f ^ g is unfolded
proof end;

theorem Th32: :: SPPOL_2:32
for f being FinSequence of (TOP-REAL 2)
for p being Point of (TOP-REAL 2)
for n being Nat st f is unfolded & p in LSeg (f,n) holds
Ins (f,n,p) is unfolded
proof end;

theorem Th33: :: SPPOL_2:33
for f being FinSequence of (TOP-REAL 2) st len f <= 2 holds
f is s.n.c.
proof end;

Lm6: for p, q being Point of (TOP-REAL 2) holds <*p,q*> is s.n.c.
proof end;

Lm7: for f being FinSequence of (TOP-REAL 2)
for n being Nat st f is s.n.c. holds
f | n is s.n.c.
proof end;

Lm8: for f being FinSequence of (TOP-REAL 2)
for n being Nat st f is s.n.c. holds
f /^ n is s.n.c.
proof end;

registration
let f be s.n.c. FinSequence of (TOP-REAL 2);
let n be Nat;
cluster f | n -> s.n.c. for FinSequence of (TOP-REAL 2);
coherence
for b1 being FinSequence of (TOP-REAL 2) st b1 = f | n holds
b1 is s.n.c. by Lm7;
cluster f /^ n -> s.n.c. for FinSequence of (TOP-REAL 2);
coherence
for b1 being FinSequence of (TOP-REAL 2) st b1 = f /^ n holds
b1 is s.n.c. by Lm8;
end;

Lm9: for f being FinSequence of (TOP-REAL 2)
for p being Point of (TOP-REAL 2) st f is s.n.c. holds
f -: p is s.n.c.
proof end;

registration
let f be s.n.c. FinSequence of (TOP-REAL 2);
let p be Point of (TOP-REAL 2);
cluster f -: p -> s.n.c. ;
coherence
f -: p is s.n.c. by Lm9;
end;

theorem Th34: :: SPPOL_2:34
for f being FinSequence of (TOP-REAL 2)
for p being Point of (TOP-REAL 2) st p in rng f & f is s.n.c. holds
f :- p is s.n.c.
proof end;

theorem Th35: :: SPPOL_2:35
for f being FinSequence of (TOP-REAL 2) st f is s.n.c. holds
Rev f is s.n.c.
proof end;

theorem Th36: :: SPPOL_2:36
for f, g being FinSequence of (TOP-REAL 2) st f is s.n.c. & g is s.n.c. & L~ f misses L~ g & ( for i being Nat st 1 <= i & i + 2 <= len f holds
LSeg (f,i) misses LSeg ((f /. (len f)),(g /. 1)) ) & ( for i being Nat st 2 <= i & i + 1 <= len g holds
LSeg (g,i) misses LSeg ((f /. (len f)),(g /. 1)) ) holds
f ^ g is s.n.c.
proof end;

theorem Th37: :: SPPOL_2:37
for f being FinSequence of (TOP-REAL 2)
for p being Point of (TOP-REAL 2)
for n being Nat st f is unfolded & f is s.n.c. & p in LSeg (f,n) & not p in rng f holds
Ins (f,n,p) is s.n.c.
proof end;

registration
cluster <*> the carrier of (TOP-REAL 2) -> special ;
coherence
<*> the carrier of (TOP-REAL 2) is special ;
end;

registration
let p be Point of (TOP-REAL 2);
cluster <*p*> -> special for FinSequence of (TOP-REAL 2);
coherence
for b1 being FinSequence of (TOP-REAL 2) st b1 = <*p*> holds
b1 is special
proof end;
end;

theorem Th38: :: SPPOL_2:38
for p, q being Point of (TOP-REAL 2) st ( p `1 = q `1 or p `2 = q `2 ) holds
<*p,q*> is special
proof end;

Lm10: for f being FinSequence of (TOP-REAL 2)
for n being Nat st f is special holds
f | n is special
proof end;

Lm11: for f being FinSequence of (TOP-REAL 2)
for n being Nat st f is special holds
f /^ n is special
proof end;

registration
let f be special FinSequence of (TOP-REAL 2);
let n be Nat;
cluster f | n -> special for FinSequence of (TOP-REAL 2);
coherence
for b1 being FinSequence of (TOP-REAL 2) st b1 = f | n holds
b1 is special by Lm10;
cluster f /^ n -> special for FinSequence of (TOP-REAL 2);
coherence
for b1 being FinSequence of (TOP-REAL 2) st b1 = f /^ n holds
b1 is special by Lm11;
end;

theorem Th39: :: SPPOL_2:39
for f being FinSequence of (TOP-REAL 2)
for p being Point of (TOP-REAL 2) st p in rng f & f is special holds
f :- p is special
proof end;

Lm12: for f being FinSequence of (TOP-REAL 2)
for p being Point of (TOP-REAL 2) st f is special holds
f -: p is special
proof end;

registration
let f be special FinSequence of (TOP-REAL 2);
let p be Point of (TOP-REAL 2);
cluster f -: p -> special ;
coherence
f -: p is special by Lm12;
end;

theorem Th40: :: SPPOL_2:40
for f being FinSequence of (TOP-REAL 2) st f is special holds
Rev f is special
proof end;

Lm13: for f, g being FinSequence of (TOP-REAL 2) st f is special & g is special & ( (f /. (len f)) `1 = (g /. 1) `1 or (f /. (len f)) `2 = (g /. 1) `2 ) holds
f ^ g is special
proof end;

theorem Th41: :: SPPOL_2:41
for f being FinSequence of (TOP-REAL 2)
for p being Point of (TOP-REAL 2)
for n being Nat st f is special & p in LSeg (f,n) holds
Ins (f,n,p) is special
proof end;

theorem Th42: :: SPPOL_2:42
for f being FinSequence of (TOP-REAL 2)
for q being Point of (TOP-REAL 2) st q in rng f & 1 <> q .. f & q .. f <> len f & f is unfolded & f is s.n.c. holds
(L~ (f -: q)) /\ (L~ (f :- q)) = {q}
proof end;

theorem Th43: :: SPPOL_2:43
for p, q being Point of (TOP-REAL 2) st p <> q & ( p `1 = q `1 or p `2 = q `2 ) holds
<*p,q*> is being_S-Seq by FINSEQ_3:94, FINSEQ_1:44, Lm2, Lm6, Th38;

definition
mode S-Sequence_in_R2 is being_S-Seq FinSequence of (TOP-REAL 2);
end;

registration
let f be S-Sequence_in_R2;
cluster Rev f -> being_S-Seq for FinSequence of (TOP-REAL 2);
coherence
for b1 being FinSequence of (TOP-REAL 2) st b1 = Rev f holds
b1 is being_S-Seq
proof end;
end;

theorem :: SPPOL_2:44
for i being Nat
for f being S-Sequence_in_R2 st i in dom f holds
f /. i in L~ f
proof end;

theorem :: SPPOL_2:45
for p, q being Point of (TOP-REAL 2) st p <> q & ( p `1 = q `1 or p `2 = q `2 ) holds
LSeg (p,q) is being_S-P_arc
proof end;

Lm14: for f being FinSequence of (TOP-REAL 2)
for p being Point of (TOP-REAL 2) st p in rng f holds
L~ (f -: p) c= L~ f
proof end;

Lm15: for f being FinSequence of (TOP-REAL 2)
for p being Point of (TOP-REAL 2) st p in rng f holds
L~ (f :- p) c= L~ f
proof end;

theorem Th46: :: SPPOL_2:46
for p being Point of (TOP-REAL 2)
for f being S-Sequence_in_R2 st p in rng f & p .. f <> 1 holds
f -: p is being_S-Seq
proof end;

theorem :: SPPOL_2:47
for p being Point of (TOP-REAL 2)
for f being S-Sequence_in_R2 st p in rng f & p .. f <> len f holds
f :- p is being_S-Seq
proof end;

theorem Th48: :: SPPOL_2:48
for p being Point of (TOP-REAL 2)
for i being Nat
for f being S-Sequence_in_R2 st p in LSeg (f,i) & not p in rng f holds
Ins (f,i,p) is being_S-Seq
proof end;

registration
cluster being_S-P_arc for Element of bool the carrier of (TOP-REAL 2);
existence
ex b1 being Subset of (TOP-REAL 2) st b1 is being_S-P_arc
proof end;
end;

theorem :: SPPOL_2:49
for P being Subset of (TOP-REAL 2)
for p1, p2 being Point of (TOP-REAL 2) st P is_S-P_arc_joining p1,p2 holds
P is_S-P_arc_joining p2,p1
proof end;

definition
let p1, p2 be Point of (TOP-REAL 2);
let P be Subset of (TOP-REAL 2);
pred p1,p2 split P means :: SPPOL_2:def 1
( p1 <> p2 & ex f1, f2 being S-Sequence_in_R2 st
( p1 = f1 /. 1 & p1 = f2 /. 1 & p2 = f1 /. (len f1) & p2 = f2 /. (len f2) & (L~ f1) /\ (L~ f2) = {p1,p2} & P = (L~ f1) \/ (L~ f2) ) );
end;

:: deftheorem defines split SPPOL_2:def 1 :
for p1, p2 being Point of (TOP-REAL 2)
for P being Subset of (TOP-REAL 2) holds
( p1,p2 split P iff ( p1 <> p2 & ex f1, f2 being S-Sequence_in_R2 st
( p1 = f1 /. 1 & p1 = f2 /. 1 & p2 = f1 /. (len f1) & p2 = f2 /. (len f2) & (L~ f1) /\ (L~ f2) = {p1,p2} & P = (L~ f1) \/ (L~ f2) ) ) );

theorem Th50: :: SPPOL_2:50
for P being Subset of (TOP-REAL 2)
for p1, p2 being Point of (TOP-REAL 2) st p1,p2 split P holds
p2,p1 split P
proof end;

Lm16: for P being Subset of (TOP-REAL 2)
for p1, p2, q being Point of (TOP-REAL 2)
for f1, f2 being S-Sequence_in_R2 st p1 = f1 /. 1 & p1 = f2 /. 1 & p2 = f1 /. (len f1) & p2 = f2 /. (len f2) & (L~ f1) /\ (L~ f2) = {p1,p2} & P = (L~ f1) \/ (L~ f2) & q <> p1 & q in rng f1 holds
ex g1, g2 being S-Sequence_in_R2 st
( p1 = g1 /. 1 & p1 = g2 /. 1 & q = g1 /. (len g1) & q = g2 /. (len g2) & (L~ g1) /\ (L~ g2) = {p1,q} & P = (L~ g1) \/ (L~ g2) )
proof end;

theorem Th51: :: SPPOL_2:51
for P being Subset of (TOP-REAL 2)
for p1, p2, q being Point of (TOP-REAL 2) st p1,p2 split P & q in P & q <> p1 holds
p1,q split P
proof end;

theorem Th52: :: SPPOL_2:52
for P being Subset of (TOP-REAL 2)
for p1, p2, q being Point of (TOP-REAL 2) st p1,p2 split P & q in P & q <> p2 holds
q,p2 split P
proof end;

theorem Th53: :: SPPOL_2:53
for P being Subset of (TOP-REAL 2)
for p1, p2, q1, q2 being Point of (TOP-REAL 2) st p1,p2 split P & q1 in P & q2 in P & q1 <> q2 holds
q1,q2 split P
proof end;

notation
let P be Subset of (TOP-REAL 2);
synonym special_polygonal P for being_special_polygon ;
end;

definition
let P be Subset of (TOP-REAL 2);
redefine attr P is being_special_polygon means :: SPPOL_2:def 2
 ex p1, p2 being Point of (TOP-REAL 2) st p1,p2 split P;
compatibility
( P is special_polygonal iff ex p1, p2 being Point of (TOP-REAL 2) st p1,p2 split P )
proof end;
end;

:: deftheorem defines special_polygonal SPPOL_2:def 2 :
for P being Subset of (TOP-REAL 2) holds
( P is special_polygonal iff ex p1, p2 being Point of (TOP-REAL 2) st p1,p2 split P );

definition
let r1, r2, r19, r29 be Real;
func [.r1,r2,r19,r29.] -> Subset of (TOP-REAL 2) equals :: SPPOL_2:def 3
((LSeg (|[r1,r19]|,|[r1,r29]|)) \/ (LSeg (|[r1,r29]|,|[r2,r29]|))) \/ ((LSeg (|[r2,r29]|,|[r2,r19]|)) \/ (LSeg (|[r2,r19]|,|[r1,r19]|)));
coherence
((LSeg (|[r1,r19]|,|[r1,r29]|)) \/ (LSeg (|[r1,r29]|,|[r2,r29]|))) \/ ((LSeg (|[r2,r29]|,|[r2,r19]|)) \/ (LSeg (|[r2,r19]|,|[r1,r19]|))) is Subset of (TOP-REAL 2) ;
end;

:: deftheorem defines [. SPPOL_2:def 3 :
for r1, r2, r19, r29 being Real holds [.r1,r2,r19,r29.] = ((LSeg (|[r1,r19]|,|[r1,r29]|)) \/ (LSeg (|[r1,r29]|,|[r2,r29]|))) \/ ((LSeg (|[r2,r29]|,|[r2,r19]|)) \/ (LSeg (|[r2,r19]|,|[r1,r19]|)));

registration
let n be Element of NAT ;
let p1, p2 be Point of (TOP-REAL n);
cluster LSeg (p1,p2) -> compact ;
coherence
LSeg (p1,p2) is compact ;
end;

registration
let r1, r2, r19, r29 be Real;
cluster [.r1,r2,r19,r29.] -> non empty compact ;
coherence
( not [.r1,r2,r19,r29.] is empty & [.r1,r2,r19,r29.] is compact )
proof end;
end;

theorem :: SPPOL_2:54
for r1, r2, r19, r29 being Real st r1 <= r2 & r19 <= r29 holds
[.r1,r2,r19,r29.] = { p where p is Point of (TOP-REAL 2) : ( ( p `1 = r1 & p `2 <= r29 & p `2 >= r19 ) or ( p `1 <= r2 & p `1 >= r1 & p `2 = r29 ) or ( p `1 <= r2 & p `1 >= r1 & p `2 = r19 ) or ( p `1 = r2 & p `2 <= r29 & p `2 >= r19 ) ) }
proof end;

theorem Th55: :: SPPOL_2:55
for r1, r2, r19, r29 being Real st r1 <> r2 & r19 <> r29 holds
[.r1,r2,r19,r29.] is special_polygonal
proof end;

theorem Th56: :: SPPOL_2:56
R^2-unit_square = [.0,1,0,1.] ;

registration
cluster special_polygonal for Element of bool the carrier of (TOP-REAL 2);
existence
ex b1 being Subset of (TOP-REAL 2) st b1 is special_polygonal
proof end;
end;

registration
cluster R^2-unit_square -> special_polygonal ;
coherence
R^2-unit_square is special_polygonal by Th55, Th56;
end;

registration
cluster special_polygonal for Element of bool the carrier of (TOP-REAL 2);
existence
ex b1 being Subset of (TOP-REAL 2) st b1 is special_polygonal by Th56;
cluster special_polygonal -> non empty for Element of bool the carrier of (TOP-REAL 2);
coherence
for b1 being Subset of (TOP-REAL 2) st b1 is special_polygonal holds
not b1 is empty ;
cluster special_polygonal -> non trivial for Element of bool the carrier of (TOP-REAL 2);
coherence
for b1 being Subset of (TOP-REAL 2) st b1 is special_polygonal holds
not b1 is trivial by ZFMISC_1:def 10;
end;

definition
mode Special_polygon_in_R2 is special_polygonal Subset of (TOP-REAL 2);
end;

theorem Th57: :: SPPOL_2:57
for P being Subset of (TOP-REAL 2) st P is being_S-P_arc holds
P is compact
proof end;

registration
cluster special_polygonal -> compact for Element of bool the carrier of (TOP-REAL 2);
coherence
for b1 being Special_polygon_in_R2 holds b1 is compact
proof end;
end;

theorem Th58: :: SPPOL_2:58
for P being Subset of (TOP-REAL 2) st P is special_polygonal holds
for p1, p2 being Point of (TOP-REAL 2) st p1 <> p2 & p1 in P & p2 in P holds
p1,p2 split P by Th53;

theorem :: SPPOL_2:59
for P being Subset of (TOP-REAL 2) st P is special_polygonal holds
for p1, p2 being Point of (TOP-REAL 2) st p1 <> p2 & p1 in P & p2 in P holds
ex P1, P2 being Subset of (TOP-REAL 2) st
( P1 is_S-P_arc_joining p1,p2 & P2 is_S-P_arc_joining p1,p2 & P1 /\ P2 = {p1,p2} & P = P1 \/ P2 )
proof end;