UnVarGraph
data UnVarSet
emptyUnVarSet
mkUnVarSet
varEnvDom
unionUnVarSet
unionUnVarSets
delUnVarSet
elemUnVarSet
isEmptyUnVarSet
data UnVarGraph
emptyUnVarGraph
unionUnVarGraph
unionUnVarGraphs
completeGraph
completeBipartiteGraph
neighbors
delNode