title: Euclidean theorem
text: # Euclidean theorem
  
  Euclidean theorem may refer to:
  
  * Any theorem in Euclidean geometry
  * Any theorem in Euclid's Elements, and in particular:
     * Euclid's theorem that there are infinitely many prime numbers
     * Euclid's lemma, also called Euclid's first theorem, on the prime factors of products
     * The Euclid–Euler theorem characterizing the even perfect numbers
     * Geometric mean theorem about right triangle altitude
  