reserve D for non empty set,
  f for FinSequence of D,
  g for circular FinSequence of D,
  p,p1,p2,p3,q for Element of D;

theorem Th3:
  p in rng f & q in rng f & p..f <= q..f implies p..(f-:q) = p..f
proof
A1: f-:q = f|(q..f) by FINSEQ_5:def 1;
  assume p in rng f & q in rng f & p..f <= q..f;
  then p in rng(f|(q..f)) by A1,FINSEQ_5:46;
  hence thesis by A1,FINSEQ_5:40;
end;
