ⅆn⁡wⅆ⁡zn+fn-1⁡(z)⁢ⅆn-1⁡wⅆ⁡zn-1+fn-2⁡(z)⁢ⅆn-2⁡wⅆ⁡zn-2+…+f1⁡(z)⁢ⅆ⁡wⅆ⁡z+f0⁡(z)⁢w=0