# Preserving

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**Quantum logic**— In mathematical physics and quantum mechanics, quantum logic is a set of rules for reasoning about propositions which takes the principles of quantum theory into account. This research area and its name originated in the 1936 paper by Garrett… …112

**Reduction (complexity)**— Example of a reduction from a boolean satisfiability problem to a vertex cover problem. Blue vertices form a vertex cover which corresponds to truth values. In computability theory and computational complexity theory, a reduction is a… …113

**Exotic sphere**— In differential topology, a mathematical discipline, an exotic sphere is a differentiable manifold M that is homeomorphic but not diffeomorphic to the standard Euclidean n sphere. That is, M is a sphere from the point of view of all its… …114

**Norwegian American**— Norskamerikanere …115

**Kleinian group**— In mathematics, a Kleinian group, named after Felix Klein, is a finitely generated discrete group Gamma; of orientation preserving conformal (i.e. angle preserving) maps of the open unit ball B^3 in mathbb{R}^3 to itself. Some… …116

**Z-order (curve)**— Z order, or Morton order, first proposed in 1966 by G. M. Morton, [citation|first=G. M.|last=Morton|title=A computer Oriented Geodetic Data Base; and a New Technique in File Sequencing|series=Technical Report|publisher=IBM Ltd.|location=Ottawa,… …117

**LOCKSS**— The LOCKSS (Lots of Copies Keep Stuff Safe) project, under the auspices of Stanford University, develops and supports an open source system allowing libraries to collect, preserve and provide their readers with access to material published on the …118

**Civil War Preservation Trust**— Infobox Non profit Non profit name = The Civil War Preservation Trust Non profit Non profit type = founded date = 1999 founder = location = Washington, D.C. key people = Jim Lighthizer, President area served = United States focus = American Civil …119

**Tetrahedral symmetry**— A regular tetrahedron has 12 rotational (or orientation preserving) symmetries, and a total of 24 symmetries including transformations that combine a reflection and a rotation.The group of symmetries that includes reflections is isomorphic to S 4 …120

**Mathematics of Sudoku**— The class of Sudoku puzzles consists of a partially completed row column grid of cells partitioned into N regions each of size N cells, to be filled in using a prescribed set of N distinct symbols (typically the numbers {1, ..., N}), so that each …