The category "<attach_unit_operation-gapsout_null-gapsin_np_gap>" can be expressed as follows:
attach <unit-gapsout_np_gap-gapsin_np_gap> to
attach <unit-gapsout_np_gap-gapsin_np_gap> under
attach to <unit-gapsout_null-gapsin_null>
attach under <unit-gapsout_null-gapsin_null>