L. Roversi

Flexible Affine Light Logic

Submitted to a journal - a preliminary version has been presented at the workshop ``LL-Linear Logic'', affiliated to FLoC'02, Copenhagen, 2002


At least two approaches to machine-independent characterizations of polynomially costing computations exist. One is purely proof-theoretic. It has been developed by introducing Light linear logic, and it is based on a careful control of the expressiveness of the logical rule contraction. The other approach is recursion-theoretic. It exists in various forms. Every of them is based essentially on some restrictions of both a recursion and a composition scheme, with of without the help of some typing discipline. Flexible Affine Light Logic (FALL) allows to bridge the two approaches. FALL derives from Light linear logic. It admits a polynomially costing normalization strategy. Moreover, there is an inductive embedding of the full system BC into FALL, BC being a recursive-theoretic characterization of poly-time, by Bellantoni and Cook. So, FALL is expressive enough to represent all the feasible computations. The distinguishing feature of FALL is that it is a proof-theoretic system that both embodies the quite restrictive structural constraints a` la Linear logic to control the reduction complexity, and keeps such constraints flexible enough to encode, and simulate, the more programming-oriented terms of BC. The paper fully formalizes the structure, and the properties of FALL. It also shows the details of the relation with BC, so opening the possibility for various comparisons of one approach to feasible computations vs. the other.


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