Periodic three body orbits in the case of small third mass

Near a symmetric periodic orbit of the plane circular or elliptic restricted probelm, the conditions for a symmetric periodic orbit of the plane general three body problem are reduced, under a natural nondegeneracy condition, to the vanishing of a single real valued function. The implicit function theorem and Hörmander's generalized Morse's lemma are then used to analyze the set of zeros of this function.