  Photon subtraction and addition are experimental means of generating
non-Gaussian states from Gaussian states. Coherent subtraction or addition is a
combination of photon subtractions or additions. The resultant states are quite
general non-Gaussian states. The states can be photon number entangled states
with arbitrary coefficients. We derive the entanglement conditions for several
classes of coherent subtraction or coherent addition bipartite continuous
variable states. One of the entanglement conditions is necessary and
sufficient.
