for i1, i2, j1, j2 being Nat
for G1, G2 being Go-board st Values G1 c= Values G2 & [i1,j1] in Indices G1 & [i2,j2] in Indices G2 & G1 * (i1,j1) = G2 * (i2,j2) holds
cell (G2,i2,(j2 -' 1)) c= cell (G1,i1,(j1 -' 1))