emptyVarSet, unitVarSet, mkVarSet,
extendVarSet, extendVarSetList, extendVarSet_C,
elemVarSet, varSetElems, subVarSet,
unionVarSet, unionVarSets,
intersectVarSet, intersectsVarSet, disjointVarSet,
isEmptyVarSet, delVarSet, delVarSetList, delVarSetByKey,
emptyVarSet, unitVarSet, mkVarSet,
extendVarSet, extendVarSetList, extendVarSet_C,
elemVarSet, varSetElems, subVarSet,
unionVarSet, unionVarSets,
intersectVarSet, intersectsVarSet, disjointVarSet,
isEmptyVarSet, delVarSet, delVarSetList, delVarSetByKey,