  It is known that S^4 is a union of two fishtails, and S^2 x S^2 is a union of
two cusps (glued along their boundaries). Here we prove that, for any choice of
knots K,L in S^3, performing knot surgery operations to S^4 and S^2 x S^2,
along both of the fishtails and cusps, respectively, do not change the
diffeomorphism type of these manifolds.
