order of contact
Suppose that and are smooth curves in which pass througha common point . We say that and have zeroth order contact if theirtangents at are distinct.
Suppose that and are tangent at . We may then set up a coordinatesystem in which is the origin and the axis is tangent to both curves.By the implicit function theorem
, there will be a neighborhood
of such that can be described parametrically as with and can be described parametrically as with. We then define the order of contact of and at to be the largest integer such that all partial derivatives
of and of order not greater than at are equal.