The formal foundations of Keynesianism are logically defective since the General Theory and Post Keynesians did not realize this until this day (2011).
Not only Post-New-Neo-Walrasians do Zombie-Economics, Post-New-Neo-Keynesians, too (cf. Quiggin, 2010).
Kakarot-Handtke, E. (2011). Why Post Keynesianism is Not Yet a Science. SSRN Working Paper Series, 1966438: 1–15. URL
Quiggin, J. (2010). Zombie Economics. How Dead Ideas Still Walk Among Us. Princeton, Oxford: Princeton University Press.