Silvia Bacchelli Elena Barcucci Elisabetta Grazzini Elisa Pergola Exhaustive generation of combinatorial objects by ECO. 585-602 2004 40 Acta Inf. 8 http://dx.doi.org/10.1007/s00236-004-0139-x db/journals/acta/acta40.html#BacchelliBGP04