γ=-∫0∞ⅇ-t⁢ln⁡t⁢ⅆ⁡t=∫0∞(11+t-ⅇ-t)⁢ⅆ⁡tt=∫01(1-ⅇ-t)⁢ⅆ⁡tt-∫1∞ⅇ-t⁢ⅆ⁡tt=∫0∞(ⅇ-t1-ⅇ-t-ⅇ-tt)⁢ⅆ⁡t.