There are two types of subscript in Maple, index and literal. For further information, please visit the help page.
From the Expressions Palette, these subscripts can be entered by selecting the appropriate button.
This type of subscript is a reference to an element of a data container, it is also the type of subscript used with some operators such as the Differential Operator D. For example:
A := [4,5,6]; A; # returns 4 type( A, indexed );
In 2D Math inputting:
A + ✲ Ctrl + ⇧ Shift + _ + 1
A + ⌘ Command + ⇧ Shift + _ + 1
will display A1.
From the Expressions Palette on the left this is the with the green 'a' and pink 'n' on the left.
Typing two underscores together produces a full symbol that is not indexed. In 2D Math input, B + ⇧ Shift + _+ _ + 1 will display as B1 similar to the above indexed variable, but it is treated as a symbol:
type( B__1, symbol ); # returns "true"
From the Expressions Palette on the left this is the with the pink 'a' and pink 'n' on the right.
If you set
interface( prettyprint = 1 ):
then the Maple output will clearly distinguish between the two types of subscripts.