sentences:  Hirzebruch signature theorem
  
  In differential topology, an area of mathematics, the Hirzebruch signature theorem (sometimes called the Hirzebruch index theorem)
  is Friedrich Hirzebruch's 1954 result expressing the signature 
  of a smooth compact oriented manifold by a linear combination of Pontryagin numbers called the 
  L-genus.It was used in the proof of the Hirzebruch–Riemann–Roch theorem.