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 INT29:
  not a divides b implies not a*c divides b
  proof
    a divides a*c;
    hence thesis by INT_2:9;
  end;
