Peter Chapman James McKinna Christian Urban Mechanising a Proof of Craig's Interpolation Theorem for Intuitionistic Logic in Nominal Isabelle. 38-52 2008 AISC/MKM/Calculemus http://dx.doi.org/10.1007/978-3-540-85110-3_5 conf/aisc/2008 db/conf/aisc/aisc2008.html#ChapmanMU08