Current issues:
  - removed debugging artefacts. -fp
  - renamed <, <*, == to below, belowEq, equiv -fp
  - removed exporting transClosure and get?
Future issues:

  - simplify calculation of relation using NF assumption. -fp
    in particular, since LF is not polymorphic, substitutions do not
    need to be carried around.

CM/
WALK
sources.cm      OK -fp
	        OK -cs
subordinate.fun Q: why are we passing an composing substitutions? -fp LATER
		OK -fp
	        OK -cs
subordinate.sig OK -fp
		OK -cs
subordinate.sml OK -fp
	 	OK -cs