reserve D for non empty set;
reserve f1,f2 for FinSequence of D;
reserve i,n,n1,n2,n3,n4,n5,n6 for Element of NAT;

theorem Th2:
  (f1^f2)|(len f1 + i) = f1^(f2|i)
proof
  (f1^f2)|(len f1 + i) = (f1^f2)|Seg(len f1 + i) & f2|i = f2|Seg i by
FINSEQ_1:def 16;
  hence thesis by FINSEQ_6:14;
end;
