Abstract. Using the calculus of variations in the large, especially computing the category of the symmetric configuration space of symmetric N-body-type problems, we prove the existence of infinitely many symmetric noncollision periodic solutions about the symmetric and nonautonomous N-body-type problems under the assumptions that the symmetric potentials satisfy the strong force condition of Gordon. §1. IntroductionCalculus of variations in the large was used to study periodic solutions for N-body-type problems in the last few years. In this paper, we will consider a class of solutions of the following system of ordinary differential equations
mi~(t)+v~,V(t, xl(t),...,xN(t))=O, x~(t) Enwhere m~ > 0 for all i, and V satisfies the following conditions: We will say that a function X(t) = (xl(t),... ,xg(t)) • C2 (R, (Rk) N) is a T-periodic noncoUision solution of (1) if X(t) is a T periodic solution of (1) and xi(t) ¢ zj(t) for all i ¢ j, and t • R.The following symmetric assumption is motivated by the Keplero N-body problem and the symmetry introduced by Bessi and Coti Zelati in [1].