theorem
  for D being non empty set, p,q being FinSequence of D, i being Element
  of NAT st p c= q & 1 <= i & i <= len p holds q.i = p.i
proof
  let D be non empty set, p,q be FinSequence of D, i be Element of NAT;
  assume p c= q;
  then
A1: ex p9 being FinSequence of D st p ^ p9 = q by Th80;
  assume 1 <= i & i <= len p;
  hence thesis by A1,FINSEQ_1:64;
end;
