reserve d,i,j,k,m,n,p,q,x,k1,k2 for Nat,
  a,c,i1,i2,i3,i5 for Integer;

theorem
  5 is prime
proof
  (3 |^ ((Fermat(1)-'1) div 2)),(-1) are_congruent_mod Fermat(1) by Lm23;
  hence thesis by Th51,Th58;
end;
