Giusi Castiglione Andrea Frosini Antonio Restivo Simone Rinaldi Enumeration of L-convex polyominoes by rows and columns. 336-352 2005 347 Theor. Comput. Sci. 1-2 http://dx.doi.org/10.1016/j.tcs.2005.06.031 db/journals/tcs/tcs347.html#CastiglioneFRR05