Naming/symbol conventions

Delta stands for change, and is commonly represented by dx, dy, ect.

0 is used for origin, or first, while incremental numbers are used for a series or index.

Is there any standard practice abbreviation or symbol for "last", "previous", or "next"?

I’ve done x0 for first, and x1 for last. Or xi for initial x and xf for final x.

I’ve used x0 from previous, x1 for current and x2 for next as well.

tx for thanks!

I like the idea of xi and xf