theorem Th21: :: MATRIX13:21

for D being non empty set
for m, n being Nat
for A being Matrix of D
for nt being Element of n -tuples_on NAT
for mt being Element of m -tuples_on NAT st n = 1 & m = 1 holds
Segm (A,nt,mt) = <*<*(A * ((nt . 1),(mt . 1)))*>*>