x4⁢ⅆ4⁡wⅆ⁡x4+2⁢x3⁢ⅆ3⁡wⅆ⁡x3-(1+2⁢ν2)⁢(x2⁢ⅆ2⁡wⅆ⁡x2-x⁢ⅆ⁡wⅆ⁡x)+(ν4-4⁢ν2+x4)⁢w=0,