za,s=ⅇ34⁢π⁢ⅈ⁢2⁢τs⁢(1-ⅈ⁢a⁢λs2⁢τs+2⁢a2⁢λs2-8⁢a2⁢λs+4⁢a2+316⁢τs2+O⁡(λs3⁢τs-3)),