reserve i,j,k,n for Nat;

theorem Th6:
  for f being non empty FinSequence holds 1 in dom f & len f in dom f
proof
  let f be non empty FinSequence;
A1: len f >= 1 by NAT_1:14;
  hence 1 in dom f by FINSEQ_3:25;
  thus thesis by A1,FINSEQ_3:25;
end;
