let G be Go-board; :: thesis: LSeg (((G * ((len G),1)) + |[1,(- 1)]|),((G * ((len G),1)) - |[0,1]|)) c= (Int (cell (G,(len G),0))) \/ {((G * ((len G),1)) - |[0,1]|)}
let x be object ; :: according to TARSKI:def 3 :: thesis: ( not x in LSeg (((G * ((len G),1)) + |[1,(- 1)]|),((G * ((len G),1)) - |[0,1]|)) or x in (Int (cell (G,(len G),0))) \/ {((G * ((len G),1)) - |[0,1]|)} )
set r1 = (G * ((len G),1)) `1 ;
set s1 = (G * (1,1)) `2 ;
assume A1: x in LSeg (((G * ((len G),1)) + |[1,(- 1)]|),((G * ((len G),1)) - |[0,1]|)) ; :: thesis: x in (Int (cell (G,(len G),0))) \/ {((G * ((len G),1)) - |[0,1]|)}
then reconsider p = x as Point of (TOP-REAL 2) ;
consider r being Real such that
A2: p = ((1 - r) * ((G * ((len G),1)) + |[1,(- 1)]|)) + (r * ((G * ((len G),1)) - |[0,1]|)) and
0 <= r and
A3: r <= 1 by A1;

now :: thesis: ( ( r = 1 & p in {((G * ((len G),1)) - |[0,1]|)} ) or ( r < 1 & p in Int (cell (G,(len G),0)) ) )

per cases ( r = 1 or r < 1 ) by A3, XXREAL_0:1;

case r = 1 ; :: thesis: p in {((G * ((len G),1)) - |[0,1]|)}

then p = (0. (TOP-REAL 2)) + (1 * ((G * ((len G),1)) - |[0,1]|)) by A2, RLVECT_1:10
.= 1 * ((G * ((len G),1)) - |[0,1]|) by RLVECT_1:4
.= (G * ((len G),1)) - |[0,1]| by RLVECT_1:def 8 ;
hence p in {((G * ((len G),1)) - |[0,1]|)} by TARSKI:def 1; :: thesis: verum

end;

case r < 1 ; :: thesis: p in Int (cell (G,(len G),0))

then 1 - r > 0 by XREAL_1:50;
then A4: (G * ((len G),1)) `1 < ((G * ((len G),1)) `1) + (1 - r) by XREAL_1:29;
(G * (1,1)) `2 < ((G * (1,1)) `2) + 1 by XREAL_1:29;
then A5: ((G * (1,1)) `2) - 1 < (G * (1,1)) `2 by XREAL_1:19;
0 <> len G by MATRIX_0:def 10;
then A6: 1 <= len G by NAT_1:14;
0 <> width G by MATRIX_0:def 10;
then A7: 1 <= width G by NAT_1:14;
A8: G * ((len G),1) = |[((G * ((len G),1)) `1),((G * ((len G),1)) `2)]| by EUCLID:53
.= |[((G * ((len G),1)) `1),((G * (1,1)) `2)]| by A7, A6, GOBOARD5:1 ;
A9: Int (cell (G,(len G),0)) = { |[r9,s9]| where r9, s9 is Real : ( (G * ((len G),1)) `1 < r9 & s9 < (G * (1,1)) `2 ) } by Th21;
p = (((1 - r) * (G * ((len G),1))) + ((1 - r) * |[1,(- 1)]|)) + (r * ((G * ((len G),1)) - |[0,1]|)) by A2, RLVECT_1:def 5
.= (((1 - r) * (G * ((len G),1))) + ((1 - r) * |[1,(- 1)]|)) + ((r * (G * ((len G),1))) - (r * |[0,1]|)) by RLVECT_1:34
.= ((r * (G * ((len G),1))) + (((1 - r) * (G * ((len G),1))) + ((1 - r) * |[1,(- 1)]|))) - (r * |[0,1]|) by RLVECT_1:def 3
.= (((r * (G * ((len G),1))) + ((1 - r) * (G * ((len G),1)))) + ((1 - r) * |[1,(- 1)]|)) - (r * |[0,1]|) by RLVECT_1:def 3
.= (((r + (1 - r)) * (G * ((len G),1))) + ((1 - r) * |[1,(- 1)]|)) - (r * |[0,1]|) by RLVECT_1:def 6
.= ((G * ((len G),1)) + ((1 - r) * |[1,(- 1)]|)) - (r * |[0,1]|) by RLVECT_1:def 8
.= ((G * ((len G),1)) + |[((1 - r) * 1),((1 - r) * (- 1))]|) - (r * |[0,1]|) by EUCLID:58
.= ((G * ((len G),1)) + |[(1 - r),(r - 1)]|) - |[(r * 0),(r * 1)]| by EUCLID:58
.= |[(((G * ((len G),1)) `1) + (1 - r)),(((G * (1,1)) `2) + (r - 1))]| - |[0,r]| by A8, EUCLID:56
.= |[((((G * ((len G),1)) `1) + (1 - r)) - 0),((((G * (1,1)) `2) + (r - 1)) - r)]| by EUCLID:62
.= |[(((G * ((len G),1)) `1) + (1 - r)),(((G * (1,1)) `2) - 1)]| ;
hence p in Int (cell (G,(len G),0)) by A5, A4, A9; :: thesis: verum

end;

end;

end;

hence x in (Int (cell (G,(len G),0))) \/ {((G * ((len G),1)) - |[0,1]|)} by XBOOLE_0:def 3; :: thesis: verum