1,829 research outputs found
Accepting grammars and systems
We investigate several kinds of regulated rewriting (programmed,
matrix, with regular control, ordered, and variants thereof) and
of parallel rewriting mechanisms (Lindenmayer systems, uniformly
limited Lindenmayer systems, limited Lindenmayer systems and
scattered context grammars) as accepting devices, in contrast
with the usual generating mode.
In some cases, accepting mode turns out to be just as powerful as
generating mode, e.g. within the grammars of the Chomsky
hierarchy, within random context, regular control, L systems,
uniformly limited L systems, scattered context. Most of these
equivalences can be proved using a metatheorem on so-called
context condition grammars. In case of matrix grammars and
programmed grammars without appearance checking, a straightforward
construction leads to the desired equivalence result.
Interestingly, accepting devices are (strictly) more powerful than
their generating counterparts in case of ordered grammars,
programmed and matrix grammars with appearance checking (even
programmed grammarsm with unconditional transfer), and 1lET0L
systems. More precisely, if we admit erasing productions, we
arrive at new characterizations of the recursivley enumerable
languages, and if we do not admit them, we get new
characterizations of the context-sensitive languages.
Moreover, we supplement the published literature showing:
- The emptiness and membership problems are recursivley solvable
for generating ordered grammars, even if we admit erasing
productions.
- Uniformly limited propagating systems can be simulated by
programmed grammars without erasing and without appearance
checking, hence the emptiness and membership problems are
recursively solvable for such systems.
- We briefly discuss the degree of nondeterminism and the
degree of synchronization for devices with limited parallelism
Membership for limited ET0L languages is not decidable
In this paper, we show how to encode arbitrary enumerable set of
numbers given by register machines within limited EPT0L systems
and programmed grammars with unconditional transfer.This result
has various consequences, e.g.the existence of nonrecursive sets
generable by 1lET0L systems or by programmed grammars with
unconditional transfer. Moreover, ordered grammars are strictly
less powerful than 1lET0L systems
\u3ci\u3ePLIVA v. Mensing\u3c/i\u3e and Its Implications
The U.S. Supreme Court ruling in PLIVA Inc. v. Mensing will immunize generic drug manufacturers facing failure-to-warn claims from state-law liability, and may also have implications for preemption jurisprudence more generally, says attorney Brian Wolfman and co-author Dena Feldman in this BNA Insight. The authors analyze the ruling, and offer their views on the questions that PLIVA raises about the ongoing vitality of the presumption against preemption, the standard for determining ‘‘impossibility’’ preemption, and the propriety of deference to an agency’s views on preemption
Misselling through agents
This paper analyzes the implications of the inherent conflict between two tasks performed by direct marketing agents: prospecting for customers and advising on the product's "suitability" for the specific needs of customers. When structuring sales-force compensation, firms trade off the expected losses from "misselling" unsuitable products with the agency costs of providing marketing incentives. We characterize how the equilibrium amount of misselling (and thus the scope of policy intervention) depends on features of the agency problem including: the internal organization of a firm's sales process, the transparency of its commission structure, and the steepness of its agents' sales incentives. JEL Classification: D18 (Consumer Protection), D83 (Search; Learning; Information and Knowledge), M31 (Marketing), M52 (Compensation and Compensation Methods and Their Effects)
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