List the names and types of all variables currently defined.
If the user types ``listvars a'', then more detailed information will be displayed. If ``listvars a a'' is typed, then even more detail is provided. This extra detail describes the makeup of a computation, the base ring of each variable, and whether a variable has been ``marked for destruction''.
If ``R'' is a user defined variable which is a ring, its type is displayed as a ``matrix''. This is because when a ring is created, it is created with an ``anonymous'' name, and the value returned is actually an ideal (remember, this means a matrix with one row) consisting of the variables in the ring. See Chapter 5 for more details.