A question about the infinity integration

Hello

I made the mablab code for the integration as

syms x y

fx1=exp(i*y*(x-1))/y; fx2=exp(i*y*(x+1))/y; fx11=int(fx1,y); fx22=int(fx2,y);

fxx=i/(2*pi)*(-fx11+fx22);

But the answer shows that

fx11=Ei(y*(x*i - i));

and fx22-fx11 is like - Ei(y*(x*i - i)) + Ei(y*(x*i + i))

Does anyone know what is the capital E here, is there another proper way to do the integration?

Thanks!