Peter B. Andrews Chad E. Brown Frank Pfenning Matthew Bishop Sunil Issar Hongwei Xi ETPS: A System to Help Students Write Formal Proofs. 75-92 2004 32 J. Autom. Reasoning 1 http://dx.doi.org/10.1023/B:JARS.0000021871.18776.94 db/journals/jar/jar32.html#AndrewsBPBIX04