Check.scm, and supporting libraries
sexp-tree.ss,
matching.ss,
and list.ss.
The libraries are packaged as MzScheme modules:
(module <module-name> <underlying-language>
(provide <name-to-export> ...)
<library-code> ...
)
If you want to use them independently of the checker,
import with (require "<file-name>").
To use them in other schemes (without learning their module systems)
remove the module wrapping and use (load "<file-name>").