theorem Th12: :: MATRIX12:12

for k, l, n being Nat
for K being comRing st l in dom (1. (K,n)) & k in dom (1. (K,n)) holds
( ILine ((1. (K,n)),l,k) is invertible & (ILine ((1. (K,n)),l,k)) ~ = ILine ((1. (K,n)),l,k) )