Polyvios Pratikakis Jeffrey S. Foster Michael Hicks Iulian Neamtiu Formalizing Soundness of Contextual Effects. 262-277 2008 TPHOLs http://dx.doi.org/10.1007/978-3-540-71067-7_22 conf/tphol/2008 db/conf/tphol/tphol2008.html#PratikakisFHN08