Editing Central limit theorem (section)

===Random walk on a crystal lattice===

The central limit theorem may be established for the simple [[random walk]] on a crystal lattice (an infinite-fold abelian covering graph over a finite graph), and is used for design of crystal structures.<ref>{{cite book |last1=Kotani |first1=M. |last2=Sunada |first2=Toshikazu |author-link2=Toshikazu Sunada |date=2003 |title=Spectral geometry of crystal lattices |publisher=Contemporary Math |volume=338 |pages=271–305 |isbn=978-0-8218-4269-0}}</ref><ref>{{cite book |author-link=Toshikazu Sunada |last=Sunada |first=Toshikazu |date=2012 |title=Topological Crystallography – With a View Towards Discrete Geometric Analysis|series=Surveys and Tutorials in the Applied Mathematical Sciences |volume=6 |publisher=Springer |isbn=978-4-431-54177-6}}</ref>