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

theorem Th50:
  Fermat(0) = 3
proof
  Fermat(0) = 2 |^ 1 + 1 by NEWTON:4
    .= 2 + 1;
  hence thesis;
end;
