Reseña: Fibonacci numbers and the Stern-Brocot tree in Coq

Se ha publicado un artículo de razonamiento formalizado en Coq titulado Fibonacci numbers and the Stern-Brocot tree in Coq.

Sus autor es José Grimm (del Marelle Team en el Inria, Sophia-Antipolis Méditerranée).

Su resumen es

In this paper, we study the representation of a number by some other numbers. For instance, an integer may be represented uniquely as a sum of powers of two; if each power of two is allowed to appear at most twice, the number of representations is s(n), a sequence studied by Dijkstra, that has many nice properties proved here with the use of the proof assistant Coq. It happens that every rational number x is uniquely the quotient s(n)/s(n+1) as noticed by Stern, and that the integer n is related to the continued fraction expansion of x. It happens that by reverting the bits on n, one gets a sequence of rational numbers with increasing denominators that goes from 1 to x and becomes nearer at each iteration; this was studied by Brocot, whence the name Stern-Brocot tree. An integer can also be represented as a sum of Fibonacci numbers; we study R(n) the number of such representations; there is uniqueness for the predecessors of Fibonacci numbers; there is also uniqueness under additional constraints (for instance, no two consecutive Fibonacci numbers can be used, or no two consecutive numbers can be omitted).

El código de las correspondientes teorías en Coq se encuentra aquí.