theorem Th17: :: MATRIX12:17

for k, l, n, m being Nat
for K being comRing
for a being Element of K
for M, M1 being Matrix of n,m,K st l in Seg (width M) & k in Seg (width M) & n > 0 & m > 0 & M1 = M @ holds
(RLineXS (M1,l,k,a)) @ = RColXS (M,l,k,a)