# Gamma(a,x) is incomplete big Gamma(a,x) from x to oo;
# Gamma(n,0,x) is small Gamma(n,x) from 0 to x;
# Gamma(n,a,x) is small Gamma(n,x) from a to x;
# Gamma(1/2,x_) := -sqrt(pi)*erf(sqrt(x));
# Gamma(1/2,-x_) := -sqrt(pi)*i*erfi(sqrt(x));
# Gamma(0,0) := inf;
# Gamma(0,x_) = -Ei(-x)=En(1,x);
# Gamma(s_,a_,b_):=Gamma(s,a)-Gamma(s,b);

Gamma(s_,a_,b_):=Gamma(s,a)-Gamma(s,b);
Gamma(s_,a_,a_) :=0;
Gamma(s_,0,b_):=Gamma(s)-Gamma(s,b);
Gamma(s_,a_,inf) := Gamma(s,a);

Gamma(a_,0):= Gamma(a);
Gamma(a_,inf):= 0;
Gamma(0,x_) := -Ei(-x);
Gamma(1,x_):= exp(-x);

#Gamma(x_+1):=x!;
Gamma(-1/2):= -2*sqrt(pi);
Gamma(1/2):= sqrt(pi);
Gamma(3/2):= sqrt(pi)/2;
Gamma(5/2):= 3/4*sqrt(pi);
Gamma(zero):= infinity;
Gamma(-zero):= -infinity;