v 0 1 0
v 0 0 0
v 1 0 1
v 1 0 -1
vn 1 0 0
vn -1 0 0
vt 0.5 0.5
vt 0 0.5
vt 1 1
vt 1 0

f 1/1/1 4/2/1 3/3/1
f 1/2/1 2/3/1 4/4/1
f 1/3/2 3/4/2 2/1/2
f 2/4/2 3/1/2 4/2/2