reserve a, b, n for Nat,
  r for Real,
  f for FinSequence of REAL;
reserve p for Prime;

theorem Th21:
  n <> 1 implies n |-count 1 = 0
proof
  assume
A1: 1 <> n;
A2: now
    assume
A3: n |^ (0+1) divides 1;
    then n |^ 1 <= 1 by NAT_D:7;
    then n <= 1;
    then n = 0 by A1,NAT_1:25;
    then 0 divides 1 by A3;
    hence contradiction;
  end;
  n |^ 0 divides 1 by NEWTON:4;
  hence thesis by A2,Def7;
end;
