The limit is often identified as the fundamental basis of calculus. But what is
the conceptual foundation of the limit? This foundation is the notion of numbers
being arbitrarily `close' to each other, so in order to arrive at a precise denition of
convergence, distance is a natural place to start. In Euclidean spaces, we can think
of the distance between two points geometrically as the length of the line connecting
them. In order to abstract this notion and form a precise idea of distance on any
set, we need to specify what attributes are required.