reserve a,b,c,h for Integer;
reserve k,m,n for Nat;
reserve i,j,z for Integer;
reserve p for Prime;

theorem
  multiples(-1) = INT
  proof
    thus multiples(-1) c= INT;
    let x be object;
    assume x in INT;
    then reconsider x as Integer;
    x is Multiple of -1 by Def15,INT_2:12;
    hence thesis;
  end;
