Editing Expression (mathematics) (section)

===Formal expression===
{{See also|Regular expression}}
A '''formal expression''' is a kind of [[String (computer science)|string]] of [[Symbol (formal)|symbols]], created by the same [[Expression (mathematics)#Formal definition|production rules]] as standard expressions, however, they are used without regard to the meaning of the expression. In this way, two ''formal expressions'' are considered equal only if they are [[Syntax (logic)|syntactically]] equal, that is, if they are the exact same expression.<ref>{{Cite book |last=McCoy |first=Neal H. |url=https://archive.org/details/introductiontomo00mcco/page/126/mode/2up?q=%22purely+formal+expression%22 |title=Introduction To Modern Algebra |publisher=[[Allyn & Bacon]] |year=1960 |location=Boston |pages=127 |lccn=68015225}}</ref><ref>{{Cite book |last=Fraleigh |first=John B. |url=https://archive.org/details/firstcourseinabs07edfral/page/198/mode/2up?q=%22formal+sum%22 |title=A first course in abstract algebra |date=2003 |publisher=Boston : Addison-Wesley |isbn=978-0-201-76390-4}}</ref> For instance, the formal expressions "2" and "1+1" are not equal.