The category "<formation>" can be expressed as follows:

<formation>

<det-not_other-sing-indef> <formation_setting>

<det-not_other-sing-indef> <formation_setting-formation> <formation_level-formation>

<det-not_other-sing-indef> <formation_setting-subformation> <formation_level-subformation>

<formation_setting> <formation_level>