Historically and intellectually there are complex connections between phenomenology and later manifestations of existentialism. The phenomenology of Edmund Husserl was one of the major influences on Jean-Paul Sartre, although Sartre came to reject some of Husserl's most distinctive doctrines. Some of the connecting and discussed doctrines are: the defining feature of consciousness is intentionality so that every and only acts of consciousness are directed to a meant or intended object; the nature of the ego; the question of which is logically prior, essence or existence; and the possibility and adequacy of a disinterested or pure transcendental conceptualization of reality or being. Husserl's first major work in philosophy was closely connected with mathematics. In the 'Philosophy of Arithmetic' he sought an epistemological account of the origin of one's ideas, understanding and knowledge of the central concepts of arithmetic: numbers, functions, arithmetical truths and the like. With respect to being-for-others, Sartre first rejects the dualistic presuppositions of the 'problem of other minds'.