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David Carr

Publications and source records attributed to David Carr.

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Endpoint Sufficiency Behavioral Quotients

A provenance-decorated generative system may contain distinct occurrences with the same visible endpoint. The central abstraction question is therefore exact: when may provenance be forgotten without changing the lawful future? We study this question through the labeled transition system induced by lawful generation and an endpoint projection U from occurrences to visible objects. Three observation levels are separated. Enabled sufficiency preserves immediately available rule labels; trace sufficiency preserves all finite lawful rule-label traces; quotient sufficiency preserves the branching transition structure modulo endpoint equivalence. The resulting hierarchy is strict. At the linear-time level, endpoint trace sufficiency is exactly inclusion of endpoint equivalence in finite-trace equivalence. At the branching level, the canonical endpoint quotient is representative-independent exactly when endpoint equivalence is a strong bisimulation equivalence. Two canonical repairs follow. Intersecting endpoint equivalence with trace equivalence gives the greatest endpoint-respecting relation preserving finite traces. The greatest endpoint-respecting bisimulation gives the maximally coarse exact branching quotient and is universal among endpoint-respecting exact quotients. For finite systems it is computed by a terminating partition-refinement procedure initialized by endpoint classes. A self-contained application to provenance-decorated nested recursive-recombinant generation exhibits two occurrences with the same visible graph I->A->B but different enabled futures; the refinement procedure separates them in its first round. The result replaces an all-or-nothing demand to retain provenance with an exact criterion for retaining only the distinctions that remain behaviorally operative.

cs.LO

Median-Extremes Alternation

Given a finite linearly ordered set, we pair positions that are mirror images about its midpoint into bilateral shells, ordered by their distance from the center. Median-Extremes Alternation (MEA) begins with the central shell and repeatedly selects the unvisited shell having greatest radial contrast with the shell most recently engaged. We prove that this local rule has a strict unique maximizer at every step and forces the shell order 0, q, 1, q-1, 2, q-2, and so on, for both odd and even cardinalities. Parity affects only whether the central shell is a singleton or a pair. A separately supplied global orientation determines the order of the elements within every shell, yielding exactly two mirror traversals for n greater than or equal to 2 before orientation is fixed and exactly one afterward. Explicit formulas, a linear-time generation algorithm, examples, and scope conditions are given. The result replaces an earlier fixed-center distance-minimization formulation, which does not generate the canonical MEA traversal.

math.GM