15-dec-2000     15-jan-2001   - wider then database
  15-dec-2000     04-jan-2001   - overlaps but not contained within
  04-jan-2001     15-jan-2001   - overlaps but not contained within
  02-jan-2001     04-jan-2001   - overlaps and contained within

##</code><code>##

select *
  from t
  where ( c_beginning between p_beginning and p_ending      -- rule 1
       OR c_ending between p_beginning and p_ending         -- rule 2
       OR ( c_beginning < p_beginning and p_ending < c_ending ) );  -- rule 3


##</code><code>##

.............................................
             CB                CE
PB                                     PE     -- rule 1
PB                   PE                       -- rule 1
                     PB                PE     -- rule 2
                  PB     PE                   -- rule 3
PB  PE                                        -- no hit
                                        PB PE -- no hit