theorem Th26: :: MATRIXJ1:26

for i, j being Nat
for D being non empty set
for d being Element of D
for F1, F2 being FinSequence_of_Matrix of D st [i,j] in Indices (block_diagonal (F1,d)) holds
(block_diagonal (F1,d)) * (i,j) = (block_diagonal ((F1 ^ F2),d)) * (i,j)