1. I get a syntax error when I try to make a pdf!
dot -Tpdf < foo.dot > foo.pdf
Possible cause: GraphViz versions 2.32 to 2.37 have a bug that interferes with arcs ending in "\". The fix is to upgrade to GraphViz >= 2.38.
2. I composed two FSTs, and the result is blank!
Your composition probably resulted in an FST that never accepts any strings. When this happens compose returns an FST with 0 states, which displays as blank. Double check the FSTs you're trying to compose.