Famous Theorems of Mathematics
A reader requests expansion of this book to include more material. You can help by adding new material (learn how) or ask for assistance in the reading room. 
Not all of mathematics deals with proofs, as mathematics involves a rich range of human experience, including ideas, problems, patterns, mistakes and corrections. However, proofs are a very big part of modern mathematics, and today, it is generally considered that whatever statement, remark, result etc. one uses in mathematics, it is considered meaningless until is accompanied by a rigorous mathematical proof. This book is intended to contain the proofs (or sketches of proofs) of many famous theorems in mathematics in no particular order. It should be used both as a learning resource, a good practice for acquiring the skill for writing your own proofs is to study the existing ones, and for general references.
It is not however intended as a companion to any other wikibook or wikipedia articles but can complement them by providing them with links to the proofs of the theorems they contain.
One note here. There are usually many ways to solve a problem. Many times the proof used comes down to the primary definitions of terms involved. We will follow the definition given by the first major contributor.
Table of contents
High school
Undergraduate
 e is irrational
 π is irrational
 Fermat's little theorem
 Fermat's theorem on sums of two squares
 Sum of the reciprocals of the primes diverges
 Bertrand's postulate
 Law of large numbers
 Spectral Theorem
 L'Hôpital's rule
 Four color theorem
 e^{πi}+1=0
Postgraduate
Old table of contents

This section contains the table of content of the book as according to its original intentions. The material here should be either incorporated in the existing book or discarded. 
Proofs and definitions will be arranged according to the fields of mathematics:
Further reading
 Mathematical Proof  about the theory and techniques of proving mathematical theorems