theorem :: GOBOARD1:18

for n, m, k being Nat
for G being Go-board st width G = m + 1 & m > 0 & k in Seg m & n in dom G holds
( (DelCol (G,1)) * (n,k) = G * (n,(k + 1)) & 1 in Seg (width G) ) by MATRIX_0:72;