proposition: Lemma FR_fib_sum8 i: FR(fib (i + 6) + 4) = (i.+3)./2.
proof: Proof. have ha : 5 <i +6 by apply (leq_trans (leqnn 6)); apply: leq_addl. move: (FR_fib_sum3 (leqnn 4) ha); rewrite - addnA => ->. by rewrite addn0 (addnA i 2 4) addnK addn2 addn1 /=. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq path fintype div bigop binomial) mathcomp(prime finset ssralg ssrnum ssrint)