# McShane's identity

In geometric topology, McShane's identity for a once punctured torus ${\displaystyle \mathbb {T} }$ with a complete, finite-volume hyperbolic structure is given by

${\displaystyle \sum _{\gamma }{\frac {1}{1+e^{\ell (\gamma )}}}={\frac {1}{2}}}$

where

• the sum is over all simple closed geodesics γ on the torus; and
• (γ) denotes the hyperbolic length of γ.

## References

• Necessary and Sufficient Conditions for McShane's Identity and Variations Ser Peow Tan, Yan Loi Wong, and Ying Zhang eprint arXiv:math/0411184 [1]
• McShane, G. Simple geodesics and a series constant over Teichmuller space. Invent. Math. 132 (1998), no. 3, 607–632.