theorem Th41:
  p in rng f implies f:-p = <*p*>^(f |-- p)
proof
  assume p in rng f;
  hence <*p*>^(f |-- p) = <*p*>^(f/^(p..f)) by FINSEQ_5:35
    .= f:-p by FINSEQ_5:def 2;
end;
