Computes the residue of an expression at a given point — the coefficient of
与 .wl 参考的差异： `Residue` and `Simplify` around Gamma poles
Residue[expr, {z, z0}]
Residue[1/z, {z, 0}]
→ 1Residue[1/(z^2 - 1), {z, 1}]
→ 1/2Residue[Exp[z]/z^3, {z, 0}]
→ 1/2Residue[1/z^2, {z, 0}]
→ 0Residue[1/(z^2 + 1), {z, I}]
→ -1/2*IResidue[Cot[z], {z, 0}]
→ 1Residue[1/(z - a), {z, a}]
→ 1