A non-learnable class of E-pattern languages
We investigate the inferrability of E-pattern languages (also known as extended or erasing pattern languages) from positive data in Gold's learning model. As the main result, our analysis yields a negative outcome for the full class of E-pattem languages-and even for the subclass of terminal-free E-pattern languages-if the corresponding terminal alphabet consists of exactly two distinct letters. Furthermore, we present a positive result for a manifest subclass of terminal-free E-pattem languages. We point out that the considered problems are closely related to fundamental questions concerning the nondeterminism of E-pattem languages. (c) 2005 Elsevier B.V. All rights reserved.
pattern languages inductive inference learning theory