Frédérique Bassino Marie-Pierre Béal Dominique Perrin Enumerative Sequences of Leaves in Rational Trees. 76-86 1997 conf/icalp/1997 ICALP db/conf/icalp/icalp97.html#BassinoBP97 http://dx.doi.org/10.1007/3-540-63165-8_166