Variabled

Checks whether the current object is ground. An object is ground if and only if it does not contain any variable. This method is guaranteed to return true if and only if the variables property of the current object refers to an empty sequence.

The sequence of Variables directly or indirectly contained in the current object. Variables are lazily returned in a non-deterministic order. Notice that no occurrence-check is performed. Thus, if a Term contains the same Variable twice or more times, then the variables sequence may contain as many occurrences of that Variable