Aho et al.ís algorithm (OneTree)
Aho, A. V., Sagiv, Y., Syzmanski, T. G., and Ullman, J. D. 1981. Inferring a tree from lowest common ancestors with an application to the optimization of relational expressions. SIAM J. Comput. 10: 405-421.
Input: set of rooted trees
1. If set is compatible (i.e., will agree on a tree), output that tree.
2. If set is not compatible, stop!