Topic
Recursively enumerable language
About: Recursively enumerable language is a research topic. Over the lifetime, 1508 publications have been published within this topic receiving 32382 citations.
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TL;DR: It is shown that the set of fixed-point combinators forms a recursively-enumerable subset of a larger set of terms that is not Recursively enumerable, and the terms of which are observationally equivalent to fixed- point combinators in any computable context.
Abstract: We show that the set of fixed-point combinators forms a recursively-enumerable subset of a larger set of terms that is (A) not recursively enumerable, and (B) the terms of which are observationally equivalent to fixed-point combinators in any computable context.
17 citations
TL;DR: This work considerably improves the result, proving that five components suffice in order to generate any recursively enumerable language.
17 citations
TL;DR: It is shown that non-returning parallel communicating grammar systems with λ-free context-free components can generate any recursively enumerable language.
17 citations
TL;DR: This work shows that the membership problem for deterministic CSs is decidable and shows that for a deterministic 1-membrane CS using only rules of type Ca → Cv, the set of reachable configurations from a given initial configuration is an effective semilinear set.
17 citations
TL;DR: The power of weak-monotonic strategies to learn recursively enumerable languages from positive data is studied and it is shown that if attention is restricted to infinite r.e. languages, then conservative strategies can identify every identifiable collection.
Abstract: Overgeneralization is a major issue in the identification of grammars for formal languages from positive data. Different formulations of generalization and specialization strategies have been proposed to address this problem, and recently there has been a flurry of activity investigating such strategies in the context of indexed families of recursive languages. The present paper studies the power of these strategies to learn recursively enumerable languages from positive data. In particular, the power of strongdmonotonic, monotonic, and weakdmonotonic (together with their dual notions modeling specialization) strategies are investigated for identification of r.e. languages. These investigations turn out to be different from the previous investigations on learning indexed families of recursive languages and at times require new proof techniques. A complete picture is provided for the relative power of each of the strategies considered. An interesting consequence is that the power of weakdmonotonic strategies is equivalent to that of conservative strategies. This result parallels the scenario for indexed classes of recursive languages. It is also shown that any identifiable collection of r.e. languages can also be identified by a strategy that exhibits the dual of weakdmonotonic property. An immediate consequence of the proof of this result is that if attention is restricted to infinite r.e. languages, then conservative strategies can identify every identifiable collection.
17 citations