This paper discusses the problems of finding similar substructures in tree Tb to tree Ta, where, both Ta and Tb are rooted and ordered trees (RO-trees), or unrooted and cyclically ordered trees (CO-trees). The authors define a maximal closest common ancestor mapping between RO-trees (CO-trees) and largest similar substructures in Tb to Ta based on these mappings, and propose two algorithms for finding one of the largest similar substructures for RO-trees and that for CO-trees. The time and space complexities of the algorithm for RO-trees are OT(NaNb) and OS(NaNb), respectively, and those of the algorithm for CO-trees are OT(mambNaNb) and OS((ma+mb)NaNb), respectively, where ma(mb) and Na(Nb) are the largest degree of a vertex and the number of vertices of Ta(Tb), respectively. [In Japanese.]
