Subscripts in Maple can be interpreted in different ways. This Tips and Techniques document explores the different types of subscripts you are able to use in Maple.
Note that this document uses Maple versions 16 and prior.
For more information on subscripts in Maple 17 and later, see:
http://www.maplesoft.com/support/help/Maple/view.aspx?path=updates/Maple17/ImprovedSubscriptHandling