theorem Th85:
  not 5 divides a|^2 - 2 & not 5 divides a|^2 + 2 &
    not 5 divides a|^2 - 3 & not 5 divides a|^2 + 3
  proof
    5 = 2*2 + 1;
    hence thesis by Th84,PEPIN:59;
  end;
