let j1, j2, i1, i2 be Element of NAT ; :: thesis: for G being Go-board st 1 <= j1 & j1 <= width G & 1 <= j2 & j2 <= width G & 1 <= i1 & i1 <= i2 & i2 <= len G holds
(G * i1,j1) `1 <= (G * i2,j2) `1
let G be Go-board; :: thesis: ( 1 <= j1 & j1 <= width G & 1 <= j2 & j2 <= width G & 1 <= i1 & i1 <= i2 & i2 <= len G implies (G * i1,j1) `1 <= (G * i2,j2) `1 )
assume that
A1: ( 1 <= j1 & j1 <= width G ) and
A2: ( 1 <= j2 & j2 <= width G ) and
A3: ( 1 <= i1 & i1 <= i2 ) and
A4: i2 <= len G ; :: thesis: (G * i1,j1) `1 <= (G * i2,j2) `1
A5: 1 <= i2 by A3, XXREAL_0:2;
then (G * i2,j1) `1 = (G * i2,1) `1 by A1, A4, GOBOARD5:3
.= (G * i2,j2) `1 by A2, A4, A5, GOBOARD5:3 ;
hence (G * i1,j1) `1 <= (G * i2,j2) `1 by A1, A3, A4, SPRECT_3:25; :: thesis: verum