Error: Nil constant used as a non-record in file record_null.dl at line 13
a(nil,nil,nil).
--^-------------
Error: Nil constant used as a non-record in file record_null.dl at line 14
a("N",nil,[nil,nil]).
-----------^----------
Error: Nil constant used as a non-record in file record_null.dl at line 15
a("N",nil,["N",[nil,nil]]).
----------------^-----------
3 errors generated, evaluation aborted
