An accent mark placed above a variable to indicate verification, checking, or a special variant in mathematical notation.
Examples
Marking a variable with a check accent (common in algebra and analysis)
\check{a} + \check{b} = \check{c}
Using check accent in function notation (often in topology or analysis)
\check{f}(x) = \sup\{g(x) : g \leq f\}
Marking dual space elements (common in functional analysis)
\text{Let } \check{v} \in V^* \text{ be a linear functional}