theorem :: GOBOARD1:12

for n, m, i being Nat
for G being Go-board st i in Seg (width G) & width G > 1 & n in dom G & m in Seg (width (DelCol (G,i))) holds
(DelCol (G,i)) * (n,m) = (Del ((Line (G,n)),i)) . m by MATRIX_0:66;