S. D. Muller, P. E. Muller, and . Schupp, The theory of ends, pushdown automata, and second-order logic, Theoretical Computer Science, vol.37, pp.51-75, 1985.
DOI : 10.1016/0304-3975(85)90087-8

I. Walukiewicz, Pushdown Processes: Games and Model Checking, BRICS Report Series, vol.3, issue.54, pp.234-263, 2001.
DOI : 10.7146/brics.v3i54.20057