Pierre Peterlongo Julien Allali Marie-France Sagot Indexing Gapped-Factors Using a Tree. 71-87 2008 19 Int. J. Found. Comput. Sci. 1 http://dx.doi.org/10.1142/S0129054108005541 db/journals/ijfcs/ijfcs19.html#PeterlongoAS08