let f be non constant standard clockwise_oriented special_circular_sequence; :: thesis:
let G be Go-board; :: thesis:
let k be Element of NAT ; :: thesis:
assume that
A1: f is_sequence_on G and
A2: 1 <= k and
A3: k + 1 <= len f and
A4: f /. k = E-max (L~ f) ; :: thesis:
consider i1, j1, i2, j2 being Element of NAT such that
A5: [i1,j1] in Indices G and
A6: f /. k = G * i1,j1 and
A7: [i2,j2] in Indices G and
A8: f /. (k + 1) = G * i2,j2 and
A9: ( ( i1 = i2 & j1 + 1 = j2 ) or ( i1 + 1 = i2 & j1 = j2 ) or ( i1 = i2 + 1 & j1 = j2 ) or ( i1 = i2 & j1 = j2 + 1 ) ) by A1, A2, A3, JORDAN8:6;
A10: (G * i1,j1) `1 = E-bound (L~ f) by A4, A6, EUCLID:56;
A11: j2 <= width G by A7, MATRIX_1:39;
take i2 ; :: thesis:
take j2 ; :: thesis:
A12: i1 <= len G by A5, MATRIX_1:39;
A13: k + 1 >= 1 + 1 by A2, XREAL_1:9;
then A14: len f >= 2 by A3, XXREAL_0:2;
k + 1 >= 1 by NAT_1:11;
then A15: k + 1 in dom f by A3, FINSEQ_3:27;
then f /. (k + 1) in L~ f by A3, A13, GOBOARD1:16, XXREAL_0:2;
then A16: (G * i1,j1) `1 >= (G * i2,j2) `1 by A8, A10, PSCOMP_1:71;
A17: ( 1 <= i1 & 1 <= j1 ) by A5, MATRIX_1:39;
A18: k < len f by A3, NAT_1:13;
then A19: k in dom f by A2, FINSEQ_3:27;
A20: i2 <= len G by A7, MATRIX_1:39;
A21: j1 <= width G by A5, MATRIX_1:39;
A22: ( 1 <= i2 & 1 <= j2 ) by A7, MATRIX_1:39;

now

per cases by A9;

suppose ( i1 = i2 & j2 + 1 = j1 ) ; :: thesis:

hence ( [i2,j2] in Indices G & [i2,(j2 + 1)] in Indices G & f /. k = G * i2,(j2 + 1) ) by A5, A6, A7; :: thesis:

end;

suppose A23: ( i2 + 1 = i1 & j2 = j1 & k <> 1 ) ; :: thesis:

reconsider k9 = k - 1 as Element of NAT by A19, FINSEQ_3:28;
k > 1 by A2, A23, XXREAL_0:1;
then k >= 1 + 1 by NAT_1:13;
then A24: k9 >= (1 + 1) - 1 by XREAL_1:11;
then consider i3, j3, i4, j4 being Element of NAT such that
A25: [i3,j3] in Indices G and
A26: f /. k9 = G * i3,j3 and
A27: [i4,j4] in Indices G and
A28: f /. (k9 + 1) = G * i4,j4 and
A29: ( ( i3 = i4 & j3 + 1 = j4 ) or ( i3 + 1 = i4 & j3 = j4 ) or ( i3 = i4 + 1 & j3 = j4 ) or ( i3 = i4 & j3 = j4 + 1 ) ) by A1, A18, JORDAN8:6;
A30: i1 = i4 by A5, A6, A27, A28, GOBOARD1:21;
k9 + 1 < len f by A3, NAT_1:13;
then k9 < len f by NAT_1:13;
then A31: k9 in dom f by A24, FINSEQ_3:27;
A32: i3 <= len G by A25, MATRIX_1:39;
A33: j1 = j4 by A5, A6, A27, A28, GOBOARD1:21;
A34: j3 <= width G by A25, MATRIX_1:39;
A35: ( 1 <= i3 & 1 <= j3 ) by A25, MATRIX_1:39;
A36: j3 = j4

proof

assume A37: j3 <> j4 ; :: thesis:

per cases by A29, A37;

suppose A38: ( i3 = i4 & j4 = j3 + 1 ) ; :: thesis:

then (G * i3,j3) `1 <> E-bound (L~ f) by A1, A18, A24, A25, A26, A27, A28, Th20;
then (G * i3,1) `1 <> E-bound (L~ f) by A32, A35, A34, GOBOARD5:3;
then (E-max (L~ f)) `1 <> E-bound (L~ f) by A4, A6, A12, A17, A21, A30, A38, GOBOARD5:3;
hence contradiction by EUCLID:56; :: thesis:

end;

suppose A39: ( i3 = i4 & j4 + 1 = j3 ) ; :: thesis:

(G * i3,j3) `1 = (G * i3,1) `1 by A32, A35, A34, GOBOARD5:3
.= (E-max (L~ f)) `1 by A4, A6, A12, A17, A21, A30, A39, GOBOARD5:3
.= E-bound (L~ f) by EUCLID:56 ;
then G * i3,j3 in E-most (L~ f) by A14, A26, A31, GOBOARD1:16, SPRECT_2:17;
then (G * i4,j4) `2 >= (G * i3,j3) `2 by A4, A28, PSCOMP_1:108;
then j4 >= j4 + 1 by A12, A17, A30, A33, A34, A39, GOBOARD5:5;
hence contradiction by NAT_1:13; :: thesis:

end;

A40: k9 + 1 = k ;
f /. k9 in L~ f by A3, A13, A31, GOBOARD1:16, XXREAL_0:2;
then A41: (G * i1,j1) `1 >= (G * i3,j3) `1 by A10, A26, PSCOMP_1:71;

now

per cases by A29, A36;

suppose i4 + 1 = i3 ; :: thesis:

then i4 >= i4 + 1 by A17, A21, A30, A33, A32, A41, A36, GOBOARD5:4;
hence contradiction by NAT_1:13; :: thesis:

end;

suppose A42: i4 = i3 + 1 ; :: thesis:

k9 + (1 + 1) <= len f by A3;
then A43: (LSeg f,k9) /\ (LSeg f,k) = {(f /. k)} by A24, A40, TOPREAL1:def 8;
( f /. k9 in LSeg f,k9 & f /. (k + 1) in LSeg f,k ) by A2, A3, A18, A24, A40, TOPREAL1:27;
then f /. (k + 1) in {(f /. k)} by A8, A23, A26, A30, A33, A36, A42, A43, XBOOLE_0:def 4;
then A44: f /. (k + 1) = f /. k by TARSKI:def 1;
i1 <> i2 by A23;
hence contradiction by A5, A6, A7, A8, A44, GOBOARD1:21; :: thesis:

end;

hence ( [i2,j2] in Indices G & [i2,(j2 + 1)] in Indices G & f /. k = G * i2,(j2 + 1) ) ; :: thesis:

end;

suppose A45: ( i2 + 1 = i1 & j2 = j1 & k = 1 ) ; :: thesis:

set k1 = len f;
k < len f by A3, NAT_1:13;
then A46: len f > 1 + 0 by A2, XXREAL_0:2;
then len f in dom f by FINSEQ_3:27;
then reconsider k9 = (len f) - 1 as Element of NAT by FINSEQ_3:28;
k + 1 >= 1 + 1 by A2, XREAL_1:9;
then len f >= 1 + 1 by A3, XXREAL_0:2;
then A47: k9 >= (1 + 1) - 1 by XREAL_1:11;
then consider i3, j3, i4, j4 being Element of NAT such that
A48: [i3,j3] in Indices G and
A49: f /. k9 = G * i3,j3 and
A50: [i4,j4] in Indices G and
A51: f /. (k9 + 1) = G * i4,j4 and
A52: ( ( i3 = i4 & j3 + 1 = j4 ) or ( i3 + 1 = i4 & j3 = j4 ) or ( i3 = i4 + 1 & j3 = j4 ) or ( i3 = i4 & j3 = j4 + 1 ) ) by A1, JORDAN8:6;
A53: f /. (len f) = f /. 1 by FINSEQ_6:def 1;
then A54: i1 = i4 by A5, A6, A45, A50, A51, GOBOARD1:21;
A55: j1 = j4 by A5, A6, A45, A53, A50, A51, GOBOARD1:21;
A56: j3 <= width G by A48, MATRIX_1:39;
k9 + 1 <= len f ;
then k9 < len f by NAT_1:13;
then A57: k9 in dom f by A47, FINSEQ_3:27;
then f /. k9 in L~ f by A3, A13, GOBOARD1:16, XXREAL_0:2;
then A58: (G * i1,j1) `1 >= (G * i3,j3) `1 by A10, A49, PSCOMP_1:71;
A59: i3 <= len G by A48, MATRIX_1:39;
A60: ( 1 <= i3 & 1 <= j3 ) by A48, MATRIX_1:39;
A61: j3 = j4

proof

assume A62: j3 <> j4 ; :: thesis:

per cases by A52, A62;

suppose A63: ( i3 = i4 & j4 = j3 + 1 ) ; :: thesis:

then (G * i3,j3) `1 <> E-bound (L~ f) by A1, A47, A48, A49, A50, A51, Th20;
then (G * i3,1) `1 <> E-bound (L~ f) by A59, A60, A56, GOBOARD5:3;
then (E-max (L~ f)) `1 <> E-bound (L~ f) by A4, A6, A12, A17, A21, A54, A63, GOBOARD5:3;
hence contradiction by EUCLID:56; :: thesis:

end;

suppose A64: ( i3 = i4 & j4 + 1 = j3 ) ; :: thesis:

(G * i3,j3) `1 = (G * i3,1) `1 by A59, A60, A56, GOBOARD5:3
.= (E-max (L~ f)) `1 by A4, A6, A12, A17, A21, A54, A64, GOBOARD5:3
.= E-bound (L~ f) by EUCLID:56 ;
then G * i3,j3 in E-most (L~ f) by A14, A49, A57, GOBOARD1:16, SPRECT_2:17;
then (G * i4,j4) `2 >= (G * i3,j3) `2 by A4, A45, A53, A51, PSCOMP_1:108;
then j4 >= j4 + 1 by A12, A17, A54, A55, A56, A64, GOBOARD5:5;
hence contradiction by NAT_1:13; :: thesis:

end;

A65: k9 + 1 = len f ;

now

per cases by A52, A61;

suppose i4 + 1 = i3 ; :: thesis:

then i4 >= i4 + 1 by A17, A21, A54, A55, A59, A58, A61, GOBOARD5:4;
hence contradiction by NAT_1:13; :: thesis:

end;

suppose A66: i4 = i3 + 1 ; :: thesis:

(len f) - 1 >= 0 by A46, XREAL_1:21;
then (len f) -' 1 = (len f) - 1 by XREAL_0:def 2;
then A67: (LSeg f,k) /\ (LSeg f,k9) = {(f . k)} by A45, JORDAN4:54
.= {(f /. k)} by A19, PARTFUN1:def 8 ;
( f /. k9 in LSeg f,k9 & f /. (k + 1) in LSeg f,k ) by A2, A3, A47, A65, TOPREAL1:27;
then f /. (k + 1) in {(f /. k)} by A8, A45, A49, A54, A55, A61, A66, A67, XBOOLE_0:def 4;
then A68: f /. (k + 1) = f /. k by TARSKI:def 1;
i1 <> i2 by A45;
hence contradiction by A5, A6, A7, A8, A68, GOBOARD1:21; :: thesis:

end;

hence ( [i2,j2] in Indices G & [i2,(j2 + 1)] in Indices G & f /. k = G * i2,(j2 + 1) ) ; :: thesis:

end;

suppose ( i2 = i1 + 1 & j1 = j2 ) ; :: thesis:

then i1 >= i1 + 1 by A17, A21, A20, A16, GOBOARD5:4;
hence ( [i2,j2] in Indices G & [i2,(j2 + 1)] in Indices G & f /. k = G * i2,(j2 + 1) ) by NAT_1:13; :: thesis:

end;

suppose A69: ( i1 = i2 & j2 = j1 + 1 ) ; :: thesis:

(G * i2,j2) `1 = (G * i2,1) `1 by A20, A22, A11, GOBOARD5:3
.= E-bound (L~ f) by A12, A17, A21, A10, A69, GOBOARD5:3 ;
then G * i2,j2 in E-most (L~ f) by A8, A14, A15, GOBOARD1:16, SPRECT_2:17;
then (G * i1,j1) `2 >= (G * i2,j2) `2 by A4, A6, PSCOMP_1:108;
then j1 >= j1 + 1 by A12, A17, A11, A69, GOBOARD5:5;
hence ( [i2,j2] in Indices G & [i2,(j2 + 1)] in Indices G & f /. k = G * i2,(j2 + 1) ) by NAT_1:13; :: thesis:

end;

hence ( [i2,(j2 + 1)] in Indices G & [i2,j2] in Indices G & f /. k = G * i2,(j2 + 1) ) ; :: thesis:
thus f /. (k + 1) = G * i2,j2 by A8; :: thesis:
reconsider f1 = f as non trivial FinSequence of (TOP-REAL 2) ;