Unlimp, Uniqueness as a Leitmotiv for Implementation

When evaluation in functional programming languages is explained using λ-calculus and/or term rewriting systems, expressions and function definitions are often defined as terms, that is as trees. Similarly, the collection of all terms is defined as a forest, that is a directed, acyclic graph where every vertex has at most one incoming edge. Concrete implementations usually drop the last restriction (and sometimes acyclicity as well), i.e. many terms can share a common subterm, meaning that different paths of subterm edges reach the same vertex in the graph.