The rules that use the category "<to_prep>" are:

<objective_mod-gapsout_null-gapsin_null>

<to_prep> <engagement_loc-gapsout_null-gapsin_null>

<compass_direction-gapsout_null-gapsin_null>

<to_prep> the <cardinal_direction>

<bearing_mod-gapsout_null-gapsin_null>

<bearing_adj> <to_prep> <bearing_spec>

<bearing_adj> <to_prep> <point_loc-gapsout_null-gapsin_null>