subscripts in CAS?

[compsystems]

Using brackets [], should index to zero and And parentheses in 1.

{a,b,c}(1)
-> a

{a,b,c}[0]
-> a

but
{a,b,c}[0] -> "Index outside range ..."

{a,b,c}(1) or {a,b,c}[1] -> a
So you have two things that do the same thing. for what?

Starting at zero, we avoid rewriting the expressions
sum(a[k]*x^k, k, 0, 5) -> sum(a[k]*x^k, k, 1, 6)