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In mathematics, an **inequation** is a statement that an inequality or a non-equality holds between two values.^{[1]}^{[2]}^{[3]} It is usually written in the form of a pair of expressions denoting the values in question, with a relational sign between them indicating the specific inequality relation. Some examples of inequations are:

In some cases, the term "inequation" can be considered synonymous to the term "inequality",^{[4]} while in other cases, an inequation is reserved only for statements whose inequality relation is "not equal to" (≠).^{[1]}^{[3]}

A shorthand notation is used for the conjunction of several inequations involving common expressions, by chaining them together.^{[1]} For example, the chain

is shorthand for

- ,

which implies that also .

In rare cases, chains without such implications about distant terms are used.
For example is shorthand for , which does not imply ^{[citation needed]} Similarly, is shorthand for , which does not imply any order of and .^{[5]}

Similar to equation solving, **inequation solving** means finding what values (numbers, functions, sets, etc.) fulfill a condition stated in the form of an inequation or a conjunction of several inequations. These expressions contain one or more *unknowns*, which are free variables for which values are sought that cause the condition to be fulfilled. To be precise, what is sought are often not necessarily actual values, but, more in general, expressions. A **solution** of the inequation is an assignment of expressions to the *unknowns* that satisfies the inequation(s); in other words, expressions such that, when they are substituted for the unknowns, make the inequations true propositions.
Often, an additional **objective** expression (i.e., an optimization equation) is given, that is to be minimized or maximized by an *optimal* solution.^{[6]}

For example,

is a conjunction of inequations, partly written as chains (where can be read as "and"); the set of its solutions is shown in blue in the picture (the red, green, and orange line corresponding to the 1st, 2nd, and 3rd conjunct, respectively). For a larger example. see Linear programming#Example.

Computer support in solving inequations is described in constraint programming; in particular, the simplex algorithm finds optimal solutions of linear inequations.^{[7]} The programming language Prolog III also supports solving algorithms for particular classes of inequalities (and other relations) as a basic language feature. For more, see constraint logic programming.

In general, the inequation is logically equivalent to the following three inequations combined:

Look up in Wiktionary, the free dictionary.inequation |

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^{a}^{b}^{c}"The Definitive Glossary of Higher Mathematical Jargon — Inequality".*Math Vault*. 2019-08-01. Retrieved 2019-12-03. **^**Thomas H. Sidebotham (2002).*The A to Z of Mathematics: A Basic Guide*. John Wiley and Sons. p. 252. ISBN 0-471-15045-2.- ^
^{a}^{b}Weisstein, Eric W. "Inequation".*mathworld.wolfram.com*. Retrieved 2019-12-03. **^**"BestMaths".*bestmaths.net*. Retrieved 2019-12-03.**^**Brian A. Davey; Hilary Ann Priestley (1990).*Introduction to Lattices and Order*. Cambridge Mathematical Textbooks. Cambridge University Press. ISBN 0-521-36766-2. LCCN 89009753.} Here: definition of a fence in exercise 1.11, p.23.**^**Stapel, Elizabeth. "Linear Programming: Introduction".*Purplemath*. Retrieved 2019-12-03.**^**"Optimization - The simplex method".*Encyclopedia Britannica*. Retrieved 2019-12-03.