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Orthogonality as a property of term rewriting systems (TRSs) describes where the reduction rules of the system are all left-linear, that is each variable occurs only once on the left hand side of each reduction rule, and there is no overlap between them, i.e. the TRS has no critical pairs.
Term rewriting systems can be employed to compute arithmetic operations on natural numbers.To this end, each such number has to be encoded as a term.The simplest encoding is the one used in the Peano axioms, based on the constant 0 (zero) and the successor function S.
A term rewriting system is said to be orthogonal if it is left-linear and is non-ambiguous. Orthogonal term rewriting systems are confluent. In certain cases, the word normal is used to mean orthogonal, particularly in the geometric sense as in the normal to a surface.
Rewriting s to t by a rule l::=r.If l and r are related by a rewrite relation, so are s and t.A simplification ordering always relates l and s, and similarly r and t.. In theoretical computer science, in particular in automated reasoning about formal equations, reduction orderings are used to prevent endless loops.
Parallel outermost and Gross-Knuth reduction are hypernormalizing for all almost-orthogonal term rewriting systems, meaning that these strategies will eventually reach a normal form if it exists, even when performing (finitely many) arbitrary reductions between successive applications of the strategy. [8]
Ellipsoidal coordinates are a three-dimensional orthogonal coordinate system (,,) that generalizes the two-dimensional elliptic coordinate system. Unlike most three-dimensional orthogonal coordinate systems that feature quadratic coordinate surfaces , the ellipsoidal coordinate system is based on confocal quadrics .
A critical pair arises in a term rewriting system when two rewrite rules overlap to yield two different terms. In more detail, ( t 1 , t 2 ) is a critical pair if there is a term t for which two different applications of a rewrite rule (either the same rule applied differently, or two different rules) yield the terms t 1 and t 2 .
Given a set E of equations between terms, the following inference rules can be used to transform it into an equivalent convergent term rewrite system (if possible): [4] [5] They are based on a user-given reduction ordering (>) on the set of all terms; it is lifted to a well-founded ordering ( ) on the set of rewrite rules by defining (s → t) (l → r) if