reserve i,j,k,n for Nat;
reserve D for non empty set,
  p for Element of D,
  f,g for FinSequence of D;

theorem
  p in rng f implies (f-:p)/.1 = f/.1
proof
  assume
A1: p in rng f;
  then 1 <= p..f by FINSEQ_4:21;
  then 1 in Seg(p..f);
  hence thesis by A1,Th43;
end;
