theorem Th92:
  p in rng f implies (Rotate(f,p))/.1 = p
proof
  assume p in rng f;
  then Rotate(f,p) =(f:-p)^((f-:p)/^1) by Def2
    .= <*p*>^(f/^p..f)^((f-:p)/^1) by FINSEQ_5:def 2
    .= <*p*>^((f/^p..f)^((f-:p)/^1)) by FINSEQ_1:32;
  hence thesis by FINSEQ_5:15;
end;
