  In this paper we prove that for any infinite word W whose set of factors is
closed under reversal, the following conditions are equivalent:
  (I) all complete returns to palindromes are palindromes;
  (II) P(n) + P(n+1) = C(n+1) - C(n) + 2 for all n, where P (resp. C) denotes
the palindromic complexity (resp. factor complexity) function of W, which
counts the number of distinct palindromic factors (resp. factors) of each
length in W.
