When calling the Standard ML library function List.map as in 'map f xs', it must be established that f is a function and xs is a list such that the function argument type and the list element type are identical. In other words, type analysis must establish a certain relation between the types. This talk presents a number of scenarios where relations between types must be established, touching upon functional languages as above, but predominantly focusing on object-oriented languages. Among the topics will be F-bounded polymorphism, type repository objects, and wildcards in the Java programming language.