Multivalued function

A multivalued function (multifunction) is a relation like a function. A multifunction associates each input with "at least one" output. A strict function associates each input with "exactly one" output. An example of a multivalued function is the square root. Every complex number (except for 0), has two square roots. Example: formula_1 could be 2 or -2 because formula_2 and formula_3.