Matt Kaufmann Konrad Slind Proof Pearl: Wellfounded Induction on the Ordinals Up to <i>epsilon</i> <sub>0</sub>. 294-301 2007 conf/tphol/2007 TPHOLs http://dx.doi.org/10.1007/978-3-540-74591-4_22 db/conf/tphol/tphol2007.html#KaufmannS07