 
Making the needle function infinitely narrower and higher, while keeping
the area constant, we get the
delta function or
delta function of Dirac δ_{a},
called after the British physicist Paul Dirac.
The simple δ is the abbreviation of δ_{0}.
The function can used for shortduring forces. It does not fit in classical
mathematics. Modern theories talk about a distribution
or a generalized function.
