Function Theory: WIKI

https://en.wikipedia.org/wiki/Cartesian_product https://en.wikipedia.org/wiki/Binary_relation

https://en.wikipedia.org/wiki/Function_(mathematics) https://en.wikipedia.org/wiki/Image_(mathematics) https://en.wikipedia.org/wiki/Inverse_image

https://en.wikipedia.org/wiki/Binary_relation https://en.wikipedia.org/wiki/Function_(mathematics) https://en.wikipedia.org/wiki/Functional_predicate https://en.wikipedia.org/wiki/Image_(mathematics)#Inverse_image https://en.wikipedia.org/wiki/Inverse_function https://en.wikipedia.org/wiki/Map_(mathematics) https://en.wikipedia.org/wiki/Mapping