# L(x,s,a) is Lerch() function ;
# =sum(x^k/(a+k)^s,k,0,inf) ;
# =integrate(t^(s-1)*exp(-a*t+t)/(exp(t)-x),t,0,inf)/gamma(s);

L(x_,s_,1):=polylog(s,x)/s;
L(1,s_,c_):=zeta(s,c);
L(-1,x_,c_):=eta(x,c);
L(a_,b_,0):=L(a,b);
L(a_,b_,inf):=0;

L(a_,b_,c_,inf):=L(a,b,c);
L(a_,b_,c_, -inf):= -L(a,b,c);
L(a_,b_,c_,0):=0;