theorem Th9: :: GOBRD13:16

for i1, i2, j1, j2 being Nat
for G1, G2 being Go-board st Values G1 c= Values G2 & 1 <= i1 & i1 <= len G1 & 1 < j1 & j1 <= width G1 & 1 <= i2 & i2 <= len G2 & 1 < j2 & j2 <= width G2 & G1 * (i1,j1) = G2 * (i2,j2) holds
(G1 * (i1,(j1 -' 1))) `2 <= (G2 * (i2,(j2 -' 1))) `2