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 set ; :: 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]|)} )
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
A3: p = ((1 - r) * ((G * (len G),1) + |[1,(- 1)]|)) + (r * ((G * (len G),1) - |[0 ,1]|)) and
A2: ( 0 <= r & r <= 1 ) by A1;
set r1 = (G * (len G),1) `1 ;
set s1 = (G * 1,1) `2 ;

now

per cases ( r = 1 or r < 1 ) by A2, 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 A3, EUCLID:33
.= 1 * ((G * (len G),1) - |[0 ,1]|) by EUCLID:31
.= (G * (len G),1) - |[0 ,1]| by EUCLID:33 ;
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 A4: 1 - r > 0 by XREAL_1:52;
(G * 1,1) `2 < ((G * 1,1) `2 ) + 1 by XREAL_1:31;
then A5: ((G * 1,1) `2 ) - 1 < (G * 1,1) `2 by XREAL_1:21;
0 <> width G by GOBOARD1:def 5;
then A6: 1 <= width G by NAT_1:14;
0 <> len G by GOBOARD1:def 5;
then A7: 1 <= len G by NAT_1:14;
A8: G * (len G),1 = |[((G * (len G),1) `1 ),((G * (len G),1) `2 )]| by EUCLID:57
.= |[((G * (len G),1) `1 ),((G * 1,1) `2 )]| by A6, A7, GOBOARD5:2 ;
A9: p = (((1 - r) * (G * (len G),1)) + ((1 - r) * |[1,(- 1)]|)) + (r * ((G * (len G),1) - |[0 ,1]|)) by A3, EUCLID:36
.= (((1 - r) * (G * (len G),1)) + ((1 - r) * |[1,(- 1)]|)) + ((r * (G * (len G),1)) - (r * |[0 ,1]|)) by EUCLID:53
.= ((r * (G * (len G),1)) + (((1 - r) * (G * (len G),1)) + ((1 - r) * |[1,(- 1)]|))) - (r * |[0 ,1]|) by EUCLID:49
.= (((r * (G * (len G),1)) + ((1 - r) * (G * (len G),1))) + ((1 - r) * |[1,(- 1)]|)) - (r * |[0 ,1]|) by EUCLID:30
.= (((r + (1 - r)) * (G * (len G),1)) + ((1 - r) * |[1,(- 1)]|)) - (r * |[0 ,1]|) by EUCLID:37
.= ((G * (len G),1) + ((1 - r) * |[1,(- 1)]|)) - (r * |[0 ,1]|) by EUCLID:33
.= ((G * (len G),1) + |[((1 - r) * 1),((1 - r) * (- 1))]|) - (r * |[0 ,1]|) by EUCLID:62
.= ((G * (len G),1) + |[(1 - r),(r - 1)]|) - |[(r * 0 ),(r * 1)]| by EUCLID:62
.= |[(((G * (len G),1) `1 ) + (1 - r)),(((G * 1,1) `2 ) + (r - 1))]| - |[0 ,r]| by A8, EUCLID:60
.= |[((((G * (len G),1) `1 ) + (1 - r)) - 0 ),((((G * 1,1) `2 ) + (r - 1)) - r)]| by EUCLID:66
.= |[(((G * (len G),1) `1 ) + (1 - r)),(((G * 1,1) `2 ) - 1)]| ;
A10: (G * (len G),1) `1 < ((G * (len G),1) `1 ) + (1 - r) by A4, XREAL_1:31;
Int (cell G,(len G),0 ) = { |[r',s']| where r', s' is Real : ( (G * (len G),1) `1 < r' & s' < (G * 1,1) `2 ) } by Th24;
hence p in Int (cell G,(len G),0 ) by A5, A9, A10; :: 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