# convert to gamma(x);


togamma(binomial(n_,k_)) := gamma(n+1)/(gamma(n-k+1)*gamma(k+1));
togamma(fallingfactorial(m_,n_)) := gamma(1+m)/gamma(m-n+1);
togamma(risingfactorial(m_,n_)) := gamma(m+n)/gamma(m);
togamma(En(n_,x_)) := x^(n-1)*gamma(1-n,x);

togamma(Ei(x_)) := -gamma(0,-x);
togamma(li(x_)) := -gamma(0, -log(x));
togamma(si(x_)) := (gamma(0,0,-i*x)-gamma(0,0,i*x))/2/i;
togamma(ci(x_)) := (gamma(0,0,-i*x)+gamma(0,0,i*x))/2;
togamma(shi(x_)) :=(gamma(0,0,-x)-gamma(0,0,x))/2;
togamma(chi(x_)) := (gamma(0,0,-x)+gamma(0,0,x))/2;
togamma(erf(x_)) := gamma(1/2,0,x^2)/sqrt(pi);
togamma(x_!) := gamma(x+1);