Nerve Axon Equations: IV The Stable and the Unstable Impulse John Evans Indiana University Mathematics Journal 1975 text pdf 10.1512/iumj.1975.24.24096 10.1512/iumj.1975.24.24096 en Indiana Univ. Math. J. 24 (1975) 1169 - 1190 state-of-the-art mathematics http://iumj.org/access/