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The standard ordering ≤ of any real interval is not a well ordering, since, for example, the open interval (,) [,] does not contain a least element. From the ZFC axioms of set theory (including the axiom of choice ) one can show that there is a well order of the reals.
By the well-ordering principle, has a minimum element such that when =, the equation is false, but true for all positive integers less than . The equation is true for n = 1 {\displaystyle n=1} , so c > 1 {\displaystyle c>1} ; c − 1 {\displaystyle c-1} is a positive integer less than c {\displaystyle c} , so the equation holds for c − 1 ...
In second-order logic, however, the well-ordering theorem is strictly stronger than the axiom of choice: from the well-ordering theorem one may deduce the axiom of choice, but from the axiom of choice one cannot deduce the well-ordering theorem. [7] There is a well-known joke about the three statements, and their relative amenability to intuition:
An axiomatic definition of the real numbers consists of defining them as the elements of a complete ordered field. [2] [3] [4] This means the following: The real numbers form a set, commonly denoted , containing two distinguished elements denoted 0 and 1, and on which are defined two binary operations and one binary relation; the operations are called addition and multiplication of real ...
In this way, one may specify a set from any given subset. One might say, "Even though the usual ordering of the real numbers does not work, it may be possible to find a different ordering of the real numbers which is a well-ordering. Then our choice function can choose the least element of every set under our unusual ordering."
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 ...
Whether you're a senior on Social Security or a worker paying into the program, the thought of rampant benefit fraud is a scary one. Unfortunately, Social Security fraud is a real thing -- and yes ...
Every well-ordered set (S,<) is order-isomorphic to the set of ordinals less than one specific ordinal number under their natural ordering. This canonical set is the order type of ( S ,<). Essentially, an ordinal is intended to be defined as an isomorphism class of well-ordered sets: that is, as an equivalence class for the equivalence relation ...