In a general relativity lecture I once saw an expression where indices were being used to mean three different things. As a power, to denote the components of a

In a general relativity lecture I once saw an expression where indices were being used to mean three different things. As a power, to denote the components of a vector and as an index over some other indexing set. Of course it was perfectly readable because there are implicit conventions about what kind of letters you can use for each of these things, and because the formula would only make sense if you read it a certain way.