1. A method comprising: executing instructions by a processor to: transform an unlabeled tree in a set of unlabeled trees to a binary labeled tree (BLT) in a set of BLTs, said unlabeled tree and BLT being elementary equivalents in that there exists a transformation between said unlabeled tree and said BLT according to a one to one and onto mapping between said set of unlabeled trees and said set of BLTs, said transformation comprising application of one or more graphical operations to a tree; and further comprising executing said instructions by said processor to transform said unlabeled tree to said BLT by: transforming said unlabeled tree to a node labeled tree, said unlabeled tree and said node labeled tree being elementary equivalents; and transforming said node labeled tree to said BLT; wherein said transforming said unlabeled tree to said node labeled tree further comprises: identifying frontier nodes of said unlabeled tree; pruning one or more terminal node children of said frontier nodes; and expressing remaining unpruned terminal nodes of said unlabeled tree as representing node labels of nodes corresponding with parent nodes of said remaining unpruned terminal nodes.