A new result is the well forgotten old one"(A Russian proverb) Annotation. An R-package "nilde" [1] for the enumeration of all existing nonnegative integer solutions of linear Diophantine equations and inequalities and related problems is presented. The software uses the approach based on a generating function of Hardy and Littlewood [2] introduced in 1966 and the algorithm proposed by Voinov and Nikulin [3] in 1997. The package proves to be useful for solving 0-1, bounded and unbounded knapsacks, subset sum problems, integer linear programs, partitioning of natural numbers, etc. The main advantage of the proposed software is that it solves all the above problems in polynomial time. Numerous examples illustrate applications of the package. Strong theoretical and empirical arguments in favor of equality P=NP are presented.