for n, m being Nat
for D being non empty set
for A, B being Matrix of n,m,D
for i being Nat st i <= n & 0 < n holds
for F being Function of (Seg i),(Seg n) ex M being Matrix of n,m,D st
( M = A +* ((B * ((idseq n) +* F)) | (Seg i)) & ( for j being Nat holds
( ( j in Seg i implies M . j = B . (F . j) ) & ( not j in Seg i implies M . j = A . j ) ) ) )