reserve a,b,c,d,x,j,k,l,m,n,o,xi,xj for Nat,
  p,q,t,z,u,v for Integer,
  a1,b1,c1,d1 for Complex;

theorem
  for a be non zero Nat, b be odd Nat holds
    2 |-count (a*b) = 2 |-count a
proof
  let a be non zero Nat, b be odd Nat;
  2 |-count (a*b) = (2 |-count a) + (2 |-count b) by INT_2:28,NAT_3:28
  .= (2 |-count a) + 0;
  hence thesis;
end;
