Jν⁡(z)⁢Jν⁡(ζ)=2π⁢∫0π/2J2⁢ν⁡(2⁢(z⁢ζ)12⁢sin⁡θ)⁢cos⁡((z-ζ)⁢cos⁡θ)⁢ⅆ⁡θ,