I have problem with instantializing a variable with subscript.
Subscript[a, i, j] = \!\(
\*UnderoverscriptBox[\(\[Product]\), \(k = i\), \(j\)]
\*SubscriptBox[\(a\), \(k\)]\);
Subscript[a, i, j] /. {i -> 1, j -> 2}
Subscript[a, 1, 2]
Why can't I instantialize ai,j by directly assigning the subscripts with 1 and 2?
