“…For example, in TOS, the following judgement Γ |= M → N → P : A informally asserts that, among other things, N and P are the weak-head normal form and the normal form of the term M, respectively. 3 For the logical framework LF, for example, its corresponding TOS has been studied [Gog99] and its inference rules are given in Appendix B. Since many meta-theoretic properties Basic f orms: Abbreviated f orms: of a type theory are concerned with its computational behaviour, it is not a surprise that TOS provides an effective approach to the meta-theory of type theories.…”