I have an sequence of half-open interval named with $$\langle\tau_i\rangle_{i=1}^3 = \langle [0, 1),[1,2),[2,3)\rangle.$$ I want to get the left and right boundary value of $\tau_2$, which is 2 and 3, respectively. I currently get them by introducing a notation of boundary value of $\tau_i:\tau_i^l$ and $\tau_i^r$. However, I want to consume alphabets as less as possible for index because I am trying to define a data structure which is tuple of 6 or 7 components and many alphabets are consumed for them.
So I want to know the following: is there any notation commonly used for getting left/right boundary value of a closed/open interval $\tau\subseteq\mathbb{R}$?