In a one-page paper from 1965 Dijkstra introduced the 'mutual exclusion problem' for n processes and discussed a solution to it. It was probably the first published concurrent algorithm. The notion, standard by now, of a 'critical section' was also introduced in this paper. Per Brinch Hansen, a pioneer in the field of concurrent computing, considers Dijkstra's "Cooperating Sequential Processes" (1965) to be the first classic paper in concurrent programming. As Brinch Hansen notes, 'Dijkstra lays the conceptual foundation for abstract concurrent programming' with that paper.