Can someone point me to how to work with an array of constants? I'm doing something related to statistics and I have a "data set" of n observations which can be considered to be n 2-tuples, all of which are constants: {{x[1], y[1]}, {x[2], y[2]}, ..., {x[n], y[n]}}. How do I declare this object in Mathematica (of arbitrary length n), so that, in the expressions I develop in Mathematica, something like x[4] is treated as a constant?