Benzmüller, Christoph; Rabe, Florian; Sutcliffe, Geoff (2008). “THF0 – The Core of the TPTP Language for Higher-Order Logic”. Automated Reasoning. Lecture Notes in Computer Science. 5195. pp. 491–506. doi:10.1007/978-3-540-71070-7_41. ISBN978-3-540-71069-1