v 0 0 0
v 1 0 0
v 1 1 0

o First
f 1 2 3

o Second
f 1 2 3
usemtl A
f 1 2 3
usemtl A
usemtl B
f 1 2 3
usemtl C
usemtl D
f 1 2 3
usemtl A
f 1 2 3

usemtl E
o Third
usemtl F
f 1 2 3
usemtl G
usemtl A
f 1 2 3
usemtl H