On the orbits of the product of two permutations

AbstractWe consider the following problem: given three partitions A,B,C of a finite set Ω, do there exist two permutations α and β such that A,B,C are induced by α, β and αβ respectively? This problem is NP-complete. However it turns out that it can be solved by a polynomial time algorithm when some relations between the number of classes of A,B,C hold

Maximal nonparabolic subgroups of the modular group

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46221/1/208_2005_Article_BF01457079.pd