"Periods" is the generic term used to designate numbers arising as integrals of algebraic functions over domains described by algebraic equations or inequalities with coefficients in . This class of numbers is larger and less well understood than the ring of algebraic numbers. However, its elements are constructible and it is conjectured that equality of any two numbers which have been expressed as periods can be verified. Most of the important constants of mathematics belong to the class of periods (Kontsevich and Zagier 2001).