for A, B being SetSequence of the carrier of (TOP-REAL 2)
for C, C1 being SetSequence of the carrier of [:(TOP-REAL 2),(TOP-REAL 2):] st ( for i being Nat holds C . i = [:(A . i),(B . i):] ) & C1 is subsequence of C holds
ex A1, B1 being SetSequence of the carrier of (TOP-REAL 2) st
( A1 is subsequence of A & B1 is subsequence of B & ( for i being Nat holds C1 . i = [:(A1 . i),(B1 . i):] ) )