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

theorem Th51:
  Fermat(1) = 5
proof
  Fermat(1) = 2 |^ (1 + 1) + 1
    .= 2 |^ 1 * 2 + 1 by NEWTON:6
    .= 2 * 2 + 1;
  hence thesis;
end;
