What is Oulipo?

Oulipo, or Ouvroir de littérature potentielle, is more of a loose gathering of writers than an actual school of literature. Composed of mostly French writers and mathematicians, those who use Oulipo seek to use very specific restrictions in their works. The group loosely translates the term “littérature potentielle” as "the seeking of new structures and patterns which may be used by writers in any way they enjoy.”
Georges Perec, was of course a member of this group, and was known for many works, such as Life: A User’s Manual (a book in which the chapters move like a knight’s tour of a chess board), Les revenentes (in which e is the only letter,) and of course, A Void (where the letter e is never used).
A Void, specifically, is an example of a lipogram, a piece of literature, poem or prose, in which a certain letter is left out. Georges Perec took this to the extreme when he decided to write an entire book in this style, and choosing the letter e to be left out, the most common letter in both the French and English language.
Other constraints include the “N+7” method, in which you replace every noun in a text with the noun seven entires after it in the dictionary. Another is the palindrome, where the text reads the same exact thing if written backwards. There is also the Macao restraint, where all letters with ascenders or descenders (such as b, d, f, j, l, p, etc.) are omitted from a text.