Inferred (dis)equalities on element variables and other changes.

src/orderedsets/DNF.scala

src/orderedsets/Main.scala

src/orderedsets/NormalForms.scala

src/orderedsets/TreeOperations.scala

src/orderedsets/Unifier.scala

src/orderedsets/UnifierMain.scala

src/orderedsets/getAlpha.scala

testcases/BinarySearchTree.scala