use join to rm extra newline after last sub label
double slashes to get correct math mode newlines

strange and yet unknown why this changed.
I updated graphviz and some other macports in the meantime.

Checking out b84f6c098798d7ff8e7cfe7732d29d368dc26ce0 and exporting a TS doesn't process slashes correctly any more, so it may have been a change in dot.
graph states are not ordered any more
extend docstring of Transitions.add_adj
add auxiliary function to derive FTS from PPP

similar to the tail of discretization.discretize