HowToCheckAExprIsTerminate

Dear all,
I am interested in the Expr class.
If I get the Expr object, how can I check whether the expression is terminate or not?
For example, the Expr: “I + 2” is not terminate,which can be reduced to “i” and “2”.
The Expr “i” is terminate, which cannot be reduced.
/Cheers.
/By Redder.