*union*- a whole resulting from combination of parts or members
- (in set theory)
- the union of two sets
*a*and*b*is that set whose members are those things which are either members of*a*or of*b*(or of both)

*urelement*- an individual or element, in the domain of a set theory, which is not a set
*universal*- completely general
- (philos)
- that (if anything) which is referred to by general terms (e.g. virtuousness)
*universal polymorphism*- (after
*[CardelliTDP]*) those kinds of polymorphism in programming languages in which a polymorphic function uses a single algorithm independent of the type of its arguments, e.g. inclusion polymorphism and parametric polymorphism. *universal characteristic*(philosophy)- an english translation of Characteristica Universalis, the name given by Leibniz to his proposed universal language in which all things be expressed and which would also be universally intelligible. See: The Method of Mathematics.
*universal quantifier*(logic)- a variable binding construct used in a logic to express the proposition that some expression is true of every element in a domain of discourse or of a type

*utopia*- An imagined perfect place or state of things, e.g.
*The Factasian Utopia*.- utopian engineering
- Term used by Karl Popper in
*[Popper45a]*for approaches to social engineering which involve first drawing a blueprint (i.e. describing the desired utopia) and then devising an implementation plan. Utopian engineering is contrasted with*historicism*, which is fatalistic and therefore may regard blueprints and plans as superfluous, and*piecemeal engineering*, which, fearful of repeating past blunders of utopian engineering, confines itself to a kind of sociological firefighting. - See also:
- piecemeal engineering