2006-11-16 wenzelm 2006-11-16 moved some fundamental concepts to General/basics.ML;
2006-11-10 wenzelm 2006-11-10 avoid strange typing problem in MosML;
2006-11-02 dixon 2006-11-02 bugfix to zipto: left and right were wrong way around.
2006-07-03 dixon 2006-07-03 fix to subst in order to allow subst when head of a term is a bound variable.
2006-06-17 dixon 2006-06-17 added interface for making term contexts.
2006-06-13 dixon 2006-06-13 Corrected search order for zippers.
2006-06-12 wenzelm 2006-06-12 tuned Seq/Envir/Unify interfaces;
2006-06-12 wenzelm 2006-06-12 made smlnj happy;
2006-06-11 dixon 2006-06-11 added updated version of IsaPlanner and substitution.