"inserted" table not allowed in derived table query

The "inserted" table not allowed in derived table query.

create trigger a on newtable

for insert

as

insert into othertable

select a,c from

(

    select distinct a,b,c from inserted

) dt

Msg 208, Level 16, State 1

Server 'DBS', Procedure 'a', Line 3

inserted not found. Specify owner.objectname or use sp_help to check whether the object exists (sp_help may produce lots of output).

Is this a documentated limitation in ASE ?