theorem Th9: :: MATRPROB:9

for k, n being Nat
for D being set
for e1, e2 being FinSequence of D ex e being FinSequence of D * st
( len e = n & ( for i being Nat st i in Seg n holds
( ( i in Seg k implies e . i = e1 ) & ( not i in Seg k implies e . i = e2 ) ) ) )