Definition distribution function
Let X be a real valued random variable (not necessarily discrete). We define its distribution function, denoted by Fx, as follows
Fx: R–>[0,1]
Fx = P(X<x)
General properties of the distribution function
1) Fx is increasing
2) Fx is right continuous
3) lim Fx(x) = 0 lim Fx(x) = 1
x->-∞ x->+∞
4) ∆Fx(x) = P(X=x)