let G be Go-board; :: thesis: for i1, j1, i2, j2 being Nat st 1 <= i1 & i1 <= len G & 1 <= j1 & j1 + 1 <= width G & 1 <= i2 & i2 <= len G & 1 <= j2 & j2 + 1 <= width G & LSeg ((G * (i1,j1)),(G * (i1,(j1 + 1)))) meets LSeg ((G * (i2,j2)),(G * (i2,(j2 + 1)))) holds
( i1 = i2 & |.(j1 - j2).| <= 1 )

let i1, j1, i2, j2 be Nat; :: thesis: ( 1 <= i1 & i1 <= len G & 1 <= j1 & j1 + 1 <= width G & 1 <= i2 & i2 <= len G & 1 <= j2 & j2 + 1 <= width G & LSeg ((G * (i1,j1)),(G * (i1,(j1 + 1)))) meets LSeg ((G * (i2,j2)),(G * (i2,(j2 + 1)))) implies ( i1 = i2 & |.(j1 - j2).| <= 1 ) )
assume that
A1: ( 1 <= i1 & i1 <= len G ) and
A2: 1 <= j1 and
A3: j1 + 1 <= width G and
A4: ( 1 <= i2 & i2 <= len G ) and
A5: 1 <= j2 and
A6: j2 + 1 <= width G ; :: thesis: ( not LSeg ((G * (i1,j1)),(G * (i1,(j1 + 1)))) meets LSeg ((G * (i2,j2)),(G * (i2,(j2 + 1)))) or ( i1 = i2 & |.(j1 - j2).| <= 1 ) )
A7: 1 <= j1 + 1 by ;
A8: j1 < width G by ;
assume LSeg ((G * (i1,j1)),(G * (i1,(j1 + 1)))) meets LSeg ((G * (i2,j2)),(G * (i2,(j2 + 1)))) ; :: thesis: ( i1 = i2 & |.(j1 - j2).| <= 1 )
then consider x being object such that
A9: x in LSeg ((G * (i1,j1)),(G * (i1,(j1 + 1)))) and
A10: x in LSeg ((G * (i2,j2)),(G * (i2,(j2 + 1)))) by XBOOLE_0:3;
reconsider p = x as Point of () by A9;
consider r1 being Real such that
A11: p = ((1 - r1) * (G * (i1,j1))) + (r1 * (G * (i1,(j1 + 1)))) and
A12: r1 >= 0 and
A13: r1 <= 1 by A9;
consider r2 being Real such that
A14: p = ((1 - r2) * (G * (i2,j2))) + (r2 * (G * (i2,(j2 + 1)))) and
A15: r2 >= 0 and
A16: r2 <= 1 by A10;
A17: 1 <= j2 + 1 by ;
A18: j2 < width G by ;
assume A19: ( not i1 = i2 or not |.(j1 - j2).| <= 1 ) ; :: thesis: contradiction
per cases ( i1 <> i2 or |.(j1 - j2).| > 1 ) by A19;
suppose i1 <> i2 ; :: thesis: contradiction
then A20: ( i1 < i2 or i2 < i1 ) by XXREAL_0:1;
A21: (G * (i2,j2)) `1 = (G * (i2,1)) `1 by
.= (G * (i2,(j2 + 1))) `1 by ;
(G * (i1,j1)) `1 = (G * (i1,1)) `1 by
.= (G * (i1,(j1 + 1))) `1 by ;
then 1 * ((G * (i1,j1)) `1) = ((1 - r1) * ((G * (i1,j1)) `1)) + (r1 * ((G * (i1,(j1 + 1))) `1))
.= (((1 - r1) * (G * (i1,j1))) `1) + (r1 * ((G * (i1,(j1 + 1))) `1)) by TOPREAL3:4
.= (((1 - r1) * (G * (i1,j1))) `1) + ((r1 * (G * (i1,(j1 + 1)))) `1) by TOPREAL3:4
.= p `1 by
.= (((1 - r2) * (G * (i2,j2))) `1) + ((r2 * (G * (i2,(j2 + 1)))) `1) by
.= ((1 - r2) * ((G * (i2,j2)) `1)) + ((r2 * (G * (i2,(j2 + 1)))) `1) by TOPREAL3:4
.= ((1 - r2) * ((G * (i2,j2)) `1)) + (r2 * ((G * (i2,(j2 + 1))) `1)) by TOPREAL3:4
.= (G * (i2,1)) `1 by
.= (G * (i2,j1)) `1 by ;
hence contradiction by A1, A2, A4, A8, A20, GOBOARD5:3; :: thesis: verum
end;
suppose A22: |.(j1 - j2).| > 1 ; :: thesis: contradiction
A23: (G * (i2,(j2 + 1))) `2 = (G * (1,(j2 + 1))) `2 by
.= (G * (i1,(j2 + 1))) `2 by ;
A24: (G * (i2,j2)) `2 = (G * (1,j2)) `2 by
.= (G * (i1,j2)) `2 by ;
A25: ((1 - r1) * ((G * (i1,j1)) `2)) + (r1 * ((G * (i1,(j1 + 1))) `2)) = (((1 - r1) * (G * (i1,j1))) `2) + (r1 * ((G * (i1,(j1 + 1))) `2)) by TOPREAL3:4
.= (((1 - r1) * (G * (i1,j1))) `2) + ((r1 * (G * (i1,(j1 + 1)))) `2) by TOPREAL3:4
.= p `2 by
.= (((1 - r2) * (G * (i2,j2))) `2) + ((r2 * (G * (i2,(j2 + 1)))) `2) by
.= ((1 - r2) * ((G * (i2,j2)) `2)) + ((r2 * (G * (i2,(j2 + 1)))) `2) by TOPREAL3:4
.= ((1 - r2) * ((G * (i1,j2)) `2)) + (r2 * ((G * (i1,(j2 + 1))) `2)) by ;
per cases ( j1 + 1 < j2 or j2 + 1 < j1 ) by ;
suppose A26: j1 + 1 < j2 ; :: thesis: contradiction
j2 < j2 + 1 by XREAL_1:29;
then (G * (i1,j2)) `2 < (G * (i1,(j2 + 1))) `2 by ;
then ( ((1 - r2) * ((G * (i1,j2)) `2)) + (r2 * ((G * (i1,j2)) `2)) = 1 * ((G * (i1,j2)) `2) & r2 * ((G * (i1,j2)) `2) <= r2 * ((G * (i1,(j2 + 1))) `2) ) by ;
then A27: (G * (i1,j2)) `2 <= ((1 - r2) * ((G * (i1,j2)) `2)) + (r2 * ((G * (i1,(j2 + 1))) `2)) by XREAL_1:6;
j1 < j1 + 1 by XREAL_1:29;
then A28: (G * (i1,j1)) `2 <= (G * (i1,(j1 + 1))) `2 by ;
1 - r1 >= 0 by ;
then ( ((1 - r1) * ((G * (i1,(j1 + 1))) `2)) + (r1 * ((G * (i1,(j1 + 1))) `2)) = 1 * ((G * (i1,(j1 + 1))) `2) & (1 - r1) * ((G * (i1,j1)) `2) <= (1 - r1) * ((G * (i1,(j1 + 1))) `2) ) by ;
then A29: ((1 - r1) * ((G * (i1,j1)) `2)) + (r1 * ((G * (i1,(j1 + 1))) `2)) <= (G * (i1,(j1 + 1))) `2 by XREAL_1:6;
(G * (i1,(j1 + 1))) `2 < (G * (i1,j2)) `2 by ;
hence contradiction by A25, A29, A27, XXREAL_0:2; :: thesis: verum
end;
suppose A30: j2 + 1 < j1 ; :: thesis: contradiction
j1 < j1 + 1 by XREAL_1:29;
then (G * (i1,j1)) `2 < (G * (i1,(j1 + 1))) `2 by ;
then ( ((1 - r1) * ((G * (i1,j1)) `2)) + (r1 * ((G * (i1,j1)) `2)) = 1 * ((G * (i1,j1)) `2) & r1 * ((G * (i1,j1)) `2) <= r1 * ((G * (i1,(j1 + 1))) `2) ) by ;
then A31: (G * (i1,j1)) `2 <= ((1 - r1) * ((G * (i1,j1)) `2)) + (r1 * ((G * (i1,(j1 + 1))) `2)) by XREAL_1:6;
j2 < j2 + 1 by XREAL_1:29;
then A32: (G * (i1,j2)) `2 <= (G * (i1,(j2 + 1))) `2 by ;
1 - r2 >= 0 by ;
then ( ((1 - r2) * ((G * (i1,(j2 + 1))) `2)) + (r2 * ((G * (i1,(j2 + 1))) `2)) = 1 * ((G * (i1,(j2 + 1))) `2) & (1 - r2) * ((G * (i1,j2)) `2) <= (1 - r2) * ((G * (i1,(j2 + 1))) `2) ) by ;
then A33: ((1 - r2) * ((G * (i1,j2)) `2)) + (r2 * ((G * (i1,(j2 + 1))) `2)) <= (G * (i1,(j2 + 1))) `2 by XREAL_1:6;
(G * (i1,(j2 + 1))) `2 < (G * (i1,j1)) `2 by ;
hence contradiction by A25, A33, A31, XXREAL_0:2; :: thesis: verum
end;
end;
end;
hence contradiction ; :: thesis: verum
end;
end;