theorem Th13: :: GOBOARD1:20

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
( k in Seg (width G) & (DelCol (G,(width G))) * (n,k) = G * (n,k) & width G in Seg (width G) ) by MATRIX_0:74;