X 4 a b

X 4 a bX 4 a bX 4 a bX 4 a b
X 4 a bX 4 a bX 4 a bX 4 a bX 4 a bX 4 a bX 4 a bX 4 a b
X 4 a bX 4 a bX 4 a bX 4 a bX 4 a bX 4 a bX 4 a bX 4 a bX 4 a bX 4 a bX 4 a bX 4 a b
X 4 a bX 4 a bX 4 a bX 4 a bX 4 a bX 4 a bX 4 a bX 4 a bX 4 a bX 4 a bX 4 a bX 4 a bX 4 a bX 4 a bX 4 a bX 4 a b
X 4 a bX 4 a bX 4 a bX 4 a bX 4 a bX 4 a bX 4 a bX 4 a b