∇2=1hξ⁢hη⁢hϕ⁢(∂∂⁡ξ⁡(hη⁢hϕhξ⁢∂∂⁡ξ)+∂∂⁡η⁡(hξ⁢hϕhη⁢∂∂⁡η)+∂∂⁡ϕ⁡(hξ⁢hηhϕ⁢∂∂⁡ϕ))=1c2⁢(ξ2-η2)⁢(∂∂⁡ξ⁡((ξ2-1)⁢∂∂⁡ξ)+∂∂⁡η⁡((1-η2)⁢∂∂⁡η)+ξ2-η2(ξ2-1)⁢(1-η2)⁢∂2∂⁡ϕ2).