
theorem Th2:
  for x,y being set, p being FinSequence of x st y in dom p holds p.y in x
proof
  let x,y be set;
  let p be FinSequence of x;
  assume y in dom p;
  then
A1: p.y in rng p by FUNCT_1:def 3;
  rng p c= x by FINSEQ_1:def 4;
  hence thesis by A1;
end;
