Homework
HW1: Prove that the number of matchings of an m x 2 box graph satisfies the
recurrence a_n = 3a_{n-1} + a_{n-2} - a_{n-3}. (A matching is a selection of
some number of edges in the graph such that no two edges share a vertex.)
HQ2: Find recursions for 1 x n and 3 x n ladder selections.