reserve a,b,c,d,m,x,n,j,k,l for Nat,
  t,u,v,z for Integer,
  f,F for FinSequence of NAT;
reserve p,q,r,s for real number;

theorem
  3 divides t-z implies 3 divides t|^n - z|^n
  proof
    3 divides (t-z) & (t-z) divides (t|^n - z|^n) implies
      3 divides (t|^n - z|^n) by INT_2:9;
    hence thesis by Th18;
  end;
