Ricci calculus
Coordinate and index notation

The author(s) will usually make it clear whether a subscript is intended as an index or as a label.

For example, in 3-D Euclidean space and using Cartesian coordinates; the coordinate vector A = (A, A, A) = (A, A, A) shows a direct correspondence between the subscripts 1, 2, 3 and the labels x, y, z. In the expression A, i is interpreted as an index ranging over the values 1, 2, 3, while the x, y, z subscripts are only labels, not variables. In the context of spacetime, the index value 0 conventionally corresponds to the label t.
language:response_language[Latin]