In mathematics, suppose C is a collection of mathematical objects (for instance sets or functions). Then we say that C is rigid if every c ∈ C is uniquely determined by less information about c than one would expect. Wikibooks Wikiversity has more about this subject: School of Mathematics Wikiquote has a collection of quotations by or about: Mathematics Look up Mathematics in Wiktionary, the free dictionary Wikimedia Commons has more media related to: Mathematics Bogomolny, Alexander: Interactive Mathematics Miscellany and Puzzles. ...

It should be emphasized that the above definition does not define a mathematical object. Instead, it describes in what sense the adjective rigid is typically used in mathematics, by mathematicians.

Some examples include:

1. Harmonic functions on the unit disk are rigid in the sense that they are uniquely determined by their boundary values.
2. By the fundamental theorem of algebra, polynomials in C are rigid in the sense that any polynomial is completely determined by its values on any countably infinite set, say N, or the unit disk.
3. Linear maps L(X,Y) between vector spaces X, Y are rigid in the sense that any L ∈ L(X,Y) is completely determined by its values on any set of basis vectors of X.
4. Mostow's rigidity theorem

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