trains is a C++ library originally written by Toby Hall. It is an implementation of Bestvina and Handel's algorithm for determining train tracks of surface homeomorphisms (Topology 34 (1995), 109-140).

As Toby only maintains a version of trains with a graphical interface for Windows, this is based on the last command-line version (trains4). Toby Hall is not responsible for bugs in this GitHub version of the software, since he is not involved in its maintenance.

The code is maintained by Jean-Luc Thiffeault. It is being updated to run on current C++ compilers.