Wn,2⁡(u,ξ)=Bi⁡(u2/3⁢ξ)⁢∑s=0n-1As⁡(ξ)u2⁢s+Bi′⁡(u2/3⁢ξ)⁢∑s=0n-2Bs⁡(ξ)u2⁢s+(4/3)+envBi⁡(u2/3⁢ξ)⁢O⁡(1u2⁢n-1),