# nonequivalence

## equivalence

[ih-kwiv-uh-luhns or for 3, ee-kwuh-vey-luhns]
noun Also, equivalency (for defs 1, 2).
1.
the state or fact of being equivalent; equality in value, force, significance, etc.
2.
an instance of this; an equivalent.
3.
Chemistry. the quality of having equal valence.
4.
Logic, Mathematics.
a.
Also called the relation between two propositions such that the second is not false when the first is true.
b.
Also called material equivalence. the relation between two propositions such that they are either both true or both false.
c.
the relation between two propositions such that each logically implies the other.
5.
(of a logical or mathematical relationship) reflexive, symmetrical, and transitive.

Origin:
1535–45; < Middle French < Medieval Latin aequivalentia, equivalent to Latin aequivalent- equivalent + -ia -ia; see -ence

nonequivalence, noun
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World English Dictionary
 equivalence or equivalency (ɪˈkwɪvələns) —n 1. the state of being equivalent or interchangeable 2. maths, logic a.  the relationship between two statements, each of which implies the other b.  Also called: biconditional the binary truth-function that takes the value true when both component sentences are true or when both are false, corresponding to English if and only if. Symbol: ≡ or ↔, as in --(p ∧ q) ≡ --p ∨ --q equivalency or equivalency —n

 nonequivalence (ˌnɒnɪˈkwɪvələns) —n 1. the relationship of being unequal or incomparable 2. logic a.  the relation between two statements only one of which can be true in any circumstances b.  a function of two statements that takes the value true only when one but not both of its arguments is true c.  a compound statement asserting that just one of its components is true

Collins English Dictionary - Complete & Unabridged 10th Edition
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Etymonline
Word Origin & History

equivalence
1540s, from Fr. équivalence, from M.L. aequivalentia, from aequivalentem (see equivalent). Related: Equivalency (1530s).
Online Etymology Dictionary, © 2010 Douglas Harper
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