IsNilpotentNearring( nr )  
A near-ring N is called nilpotent if there is a positive integer k, s.t. N^k = {0}.
The function IsNilpotentNearring tests if
the near-ring nr is nilpotent and returns the according boolean value 
true or false.
gap> IsNilpotentNearring( LibraryNearring( "V4", 4 ) ); true
GAP 3.4.4