F a b

F a bF a bF a bF a bF a bF a b
F a bF a bF a bF a bF a bF a b
F a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a bF a b