reserve i,j,k,n for Nat;
reserve D for non empty set,
  p for Element of D,
  f,g for FinSequence of D;

theorem Th42:
  p in rng f implies len(f-:p) = p..f
proof
  assume p in rng f;
  then p..f in dom f by FINSEQ_4:20;
  then p..f <= len f by FINSEQ_3:25;
  hence thesis by FINSEQ_1:59;
end;
