∫abⅇⅈ⁢x⁢t⁢q⁡t⁢ⅆ⁡t∼ⅇⅈ⁢a⁢x⁢∑s=0∞qs⁡a⁢ⅈxs+1-ⅇⅈ⁢b⁢x⁢∑s=0∞qs⁡b⁢ⅈxs+1,