theorem Th83:
  p in rng f & p..f <> 1 implies (f/^1):-p = f:-p
proof
  assume that
A1: p in rng f and
A2: p..f <> 1;
  p..f >= 1 by A1,FINSEQ_4:21;
  then p..f > 1 by A2,XXREAL_0:1;
  hence thesis by A1,Th82;
end;
