Well-founded Relation
In mathematics, a binary relation, R, is well-founded (or wellfounded) on a class X if and only if every non-empty subset of X has a minimal element with respect to R; that is, for every non-empty subset S of X, there is an element m of S such that for every element s of S, the pair (s,m) is not in R:
(Some authors include an extra condition that R is set-like, i.e., that the elements less than any given element form a set.)
Equivalently, assuming some choice, a relation is well-founded if and only if it contains no countable infinite descending chains: that is, there is no infinite sequence x0, x1, x2, ... of elements of X such that xn+1 R xn for every natural number n.
In order theory, a partial order is called well-founded if the corresponding strict order is a well-founded relation. If the order is a total order then it is called a well-order.
In set theory, a set x is called a well-founded set if the set membership relation is well-founded on the transitive closure of x. The axiom of regularity, which is one of the axioms of Zermelo–Fraenkel set theory, asserts that all sets are well-founded.
A relation R is converse well-founded, upwards well-founded or Noetherian on X, if the converse relation R-1 is well-founded on X. In this case R is also said to satisfy the ascending chain condition.
Read more about Well-founded Relation: Induction and Recursion, Examples, Other Properties, Reflexivity
Famous quotes containing the word relation:
“A theory of the middle class: that it is not to be determined by its financial situation but rather by its relation to government. That is, one could shade down from an actual ruling or governing class to a class hopelessly out of relation to government, thinking of gov’t as beyond its control, of itself as wholly controlled by gov’t. Somewhere in between and in gradations is the group that has the sense that gov’t exists for it, and shapes its consciousness accordingly.”
—Lionel Trilling (1905–1975)