theorem
  dom(p - A) = dom p implies A misses rng p
proof
A1: dom(p - A) = Seg len(p - A) by FINSEQ_1:def 3;
A2: dom p = Seg len p by FINSEQ_1:def 3;
  assume dom(p - A) = dom p;
  hence thesis by A1,A2,Th59,FINSEQ_1:6;
end;
