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

now

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

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

then p = (0. (TOP-REAL 2)) + (1 * ((G * 1,(width G)) - |[1,0 ]|)) by A2, EUCLID:33
.= 1 * ((G * 1,(width G)) - |[1,0 ]|) by EUCLID:31
.= (G * 1,(width G)) - |[1,0 ]| by EUCLID:33 ;
hence p in {((G * 1,(width G)) - |[1,0 ]|)} by TARSKI:def 1; :: thesis: verum

end;

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

then 1 - r > 0 by XREAL_1:52;
then A4: (G * 1,(width G)) `2 < ((G * 1,(width G)) `2 ) + (1 - r) by XREAL_1:31;
0 <> width G by GOBOARD1:def 5;
then A5: 1 <= width G by NAT_1:14;
0 <> len G by GOBOARD1:def 5;
then A6: 1 <= len G by NAT_1:14;
A7: G * 1,(width G) = |[((G * 1,(width G)) `1 ),((G * 1,(width G)) `2 )]| by EUCLID:57
.= |[((G * 1,1) `1 ),((G * 1,(width G)) `2 )]| by A5, A6, GOBOARD5:3 ;
A8: Int (cell G,0 ,(width G)) = { |[r9,s9]| where r9, s9 is Real : ( r9 < (G * 1,1) `1 & (G * 1,(width G)) `2 < s9 ) } by Th22;
(G * 1,1) `1 < ((G * 1,1) `1 ) + 1 by XREAL_1:31;
then A9: ((G * 1,1) `1 ) - 1 < (G * 1,1) `1 by XREAL_1:21;
p = (((1 - r) * (G * 1,(width G))) + ((1 - r) * |[(- 1),1]|)) + (r * ((G * 1,(width G)) - |[1,0 ]|)) by A2, EUCLID:36
.= (((1 - r) * (G * 1,(width G))) + ((1 - r) * |[(- 1),1]|)) + ((r * (G * 1,(width G))) - (r * |[1,0 ]|)) by EUCLID:53
.= ((r * (G * 1,(width G))) + (((1 - r) * (G * 1,(width G))) + ((1 - r) * |[(- 1),1]|))) - (r * |[1,0 ]|) by EUCLID:49
.= (((r * (G * 1,(width G))) + ((1 - r) * (G * 1,(width G)))) + ((1 - r) * |[(- 1),1]|)) - (r * |[1,0 ]|) by EUCLID:30
.= (((r + (1 - r)) * (G * 1,(width G))) + ((1 - r) * |[(- 1),1]|)) - (r * |[1,0 ]|) by EUCLID:37
.= ((G * 1,(width G)) + ((1 - r) * |[(- 1),1]|)) - (r * |[1,0 ]|) by EUCLID:33
.= ((G * 1,(width G)) + |[((1 - r) * (- 1)),((1 - r) * 1)]|) - (r * |[1,0 ]|) by EUCLID:62
.= ((G * 1,(width G)) + |[(r - 1),(1 - r)]|) - |[(r * 1),(r * 0 )]| by EUCLID:62
.= |[(((G * 1,1) `1 ) + (r - 1)),(((G * 1,(width G)) `2 ) + (1 - r))]| - |[r,0 ]| by A7, EUCLID:60
.= |[((((G * 1,1) `1 ) + (r - 1)) - r),((((G * 1,(width G)) `2 ) + (1 - r)) - 0 )]| by EUCLID:66
.= |[(((G * 1,1) `1 ) - 1),(((G * 1,(width G)) `2 ) + (1 - r))]| ;
hence p in Int (cell G,0 ,(width G)) by A4, A9, A8; :: thesis: verum

end;

end;

end;

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