I am reading a paper (to be able to implement the Baum-Welch algorithm in it) and the following notation is defined:
$ [ a_k ]_{k=i}^j ≡ (a_i, a_{i+1}, \ldots , a_j) $
$ [a(k)]_{k=i}^j ≡ (a(i), a(i+ 1), \ldots , a( j)) $
I (think) the first is shorthand of a n-tuple. I guess the second is something like that, but I don't understand the difference between the first and the second. Is this common notation something odd, or what? I am pretty rusty on my math, so if I am missing something obvious please don't hesitate to point that out.