let i1, j1, j2 be Element of NAT ; :: thesis: for G1, G2 being Go-board st Values G1 c= Values G2 & [i1,j1] in Indices G1 & 1 <= j2 & j2 <= width G2 & G1 * i1,j1 = G2 * 1,j2 holds
i1 = 1
let G1, G2 be Go-board; :: thesis: ( Values G1 c= Values G2 & [i1,j1] in Indices G1 & 1 <= j2 & j2 <= width G2 & G1 * i1,j1 = G2 * 1,j2 implies i1 = 1 )
assume that
A1: Values G1 c= Values G2 and
A2: [i1,j1] in Indices G1 and
A3: ( 1 <= j2 & j2 <= width G2 ) and
A4: G1 * i1,j1 = G2 * 1,j2 ; :: thesis: i1 = 1
set p = G1 * 1,j1;
A5: ( 1 <= j1 & j1 <= width G1 ) by A2, MATRIX_1:39;
assume A6: i1 <> 1 ; :: thesis: contradiction
1 <= i1 by A2, MATRIX_1:39;
then A7: 1 < i1 by A6, XXREAL_0:1;
i1 <= len G1 by A2, MATRIX_1:39;
then A8: (G1 * 1,j1) `1 < (G1 * i1,j1) `1 by A5, A7, GOBOARD5:4;
0 <> len G1 by GOBOARD1:def 5;
then 1 <= len G1 by NAT_1:14;
then [1,j1] in Indices G1 by A5, MATRIX_1:37;
then G1 * 1,j1 in { (G1 * i,j) where i, j is Element of NAT : [i,j] in Indices G1 } ;
then G1 * 1,j1 in Values G1 by Th7;
then G1 * 1,j1 in Values G2 by A1;
then G1 * 1,j1 in { (G2 * i,j) where i, j is Element of NAT : [i,j] in Indices G2 } by Th7;
then consider i, j being Element of NAT such that
A9: G1 * 1,j1 = G2 * i,j and
A10: [i,j] in Indices G2 ;
A11: ( 1 <= j & j <= width G2 ) by A10, MATRIX_1:39;
0 <> len G2 by GOBOARD1:def 5;
then A12: 1 <= len G2 by NAT_1:14;
then A13: (G2 * 1,j) `1 = (G2 * 1,1) `1 by A11, GOBOARD5:3
.= (G2 * 1,j2) `1 by A3, A12, GOBOARD5:3 ;
A14: i <= len G2 by A10, MATRIX_1:39;
1 <= i by A10, MATRIX_1:39;
then 1 < i by A4, A8, A9, A13, XXREAL_0:1;
hence contradiction by A4, A8, A9, A14, A11, A13, GOBOARD5:4; :: thesis: verum