In MPL you can now give a defined index another name. This is called an alias index and is used to facilitate repeated use of the same index in a vector, for example, in transportation problems. For instance:
INDEX location := (A,B,C,D,); dest := location; source := location;
This expression defines the source and dest indexes as an alias index of the location index and allows you, for example, to define the following variable:
DECISION VARIABLES ship[source,dest]