Abstract
This note discusses a hierarchy of different kind of context-free derivations by studying the corresponding Szilard languages. Especially, we introduce the leftmost and rightmost breadth-first derivations which are the counterparts of the well-known (depth-first) leftmost and rightmost derivations. It is shown that the Szilard languages related to different derivation types can be recognized by one-state automata which differ from each others by their memory devices.
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