Luca Aceto Wan J. Fokkink Anna Ingólfsdóttir Sumit Nain Bisimilarity is not finitely based over BPA with interrupt. 60-81 2006 366 Theor. Comput. Sci. 1-2 https://doi.org/10.1016/j.tcs.2006.07.003 db/journals/tcs/tcs366.html#AcetoFIN06