Editing Theorem (section)

==Layout==

A theorem and its proof are typically laid out as follows:

:''Theorem'' (name of the person who proved it, along with year of discovery or publication of the proof)
:''Statement of theorem (sometimes called the ''proposition'')''
:''Proof''
:''Description of proof''
:''End''

The end of the proof may be signaled by the letters [[Q.E.D.]] (''quod erat demonstrandum'') or by one of the [[Tombstone (typography)|tombstone]] marks, such as "□" or "∎", meaning "end of proof", introduced by [[Paul Halmos]] following their use in magazines to mark the end of an article.<ref>{{cite web |url=http://jeff560.tripod.com/set.html |title=Earliest Uses of Symbols of Set Theory and Logic |website=jeff560.tripod.com |access-date=2019-11-02 |df=dmy-all}}</ref>

The exact style depends on the author or publication. Many publications provide instructions or [[Macro (computer science)|macros]] for typesetting in the [[Style guide|house style]].

It is common for a theorem to be preceded by [[definition]]s describing the exact meaning of the terms used in the theorem. It is also common for a theorem to be preceded by a number of ''propositions'' or ''lemmas'' which are then used in the proof. However, lemmas are sometimes embedded in the proof of a theorem, either with nested proofs, or with their proofs presented after the proof of the theorem.

Corollaries to a theorem are either presented between the theorem and the proof, or directly after the proof. Sometimes, corollaries have proofs of their own that explain why they follow from the theorem.