Workaround for using functions in restricted system
If the functions are just doing SELECT statements then you can simulate them with an inline view ...

  select t.*
         , notaf.descr
  from  t
        , ( select code, descr from lookup_tbl ) notaf
  where t.col23 = notaf.code


... or a sub-query factoring clause ...

with notaf as ( select code, descr from lookup_tbl )
select t.*
         , notaf.descr
from  t
       , notaf
where t.col23 = notaf.code


--- or even a simple join (using ANSI syntax for variety!) ...

select t.*
         , lookup_tbl.descr
from  t
      join lookup_tbl
           on  t.col23 = lookup_tbl.code


You can use DUAL if the function does something computational (rather than a data lookup) but you may need to pfaff around with nested views to simulate passing parameters.