I want to use `Subscript`s to prettify a matrix and started the following way

    Subscript[a, bb] // TraditionalForm
    Subscript[a, b,b] // TraditionalForm
    Subscript[Subscript[a, b], b] // TraditionalForm

The results are
$$
a_{bb}\\
a_{b,b}\\
a_{b_b}
$$
I want to use the first type.

But, I need to create the `Subscript` $a$ with elements from a list, like so

    list = {b,c,d};
    Subscript[a, list[[1]] list[[1]]] // TraditionalForm
    Subscript[a, list[[1]], list[[1]]] // TraditionalForm
    Subscript[Subscript[a, list[[1]]], list[[1]]] // TraditionalForm

Then, the result is
$$
a_{b^2}\\
a_{b,b}\\
a_{b_b}
$$

Sticking with the first type; So, How do I prevent that $b^2$? Or, how do I erase the comma from second output?