In mathematics or logic, a finitary operation is one, like those of arithmetic, that take a number of input values to produce an output. An operation such as taking an integral of a function, in calculus, is defined in such a way as to depend on all the values of the function (infinitely many of them, in general), and is so not prima facie finitary. In the logic proposed for quantum mechanics, depending on the use of subspaces of Hilbert space as propositions, operations such as taking the intersection of subspaces are used; this in general cannot be considered a finitary operation.