pi1[z_]=3/(16Pi^2)*(5/6+13/(6z)-(1-z)(3+2z)/z g[z]+(1-z)(1-16z)/(6z) g[z]^2 - (1+2z)/(6z) (i[z]/z+2z*(1-z)D[i[z]/z,z]));
g[z_]= 1/(2z)*Log[u]/Sqrt[1-1/z]/.u ->((1-1/z)^(1/2)-1)/((1-1/z)^(1/2)+1);
i[z_]=6(Zeta[3]+4 PolyLog[3,-u]+2 PolyLog[3,u])-8(2 PolyLog[2,-u]+PolyLog[2,u])Log[u]-2(2 Log[1+u]+Log[1-u])Log[u]^2 /.u ->((1-1/z)^(1/2)-1)/((1-1/z)^(1/2)+1);
