The ↑-arrow refers to the f-structure of Figure 1: LFG c-structure and f-structure analysis of Maria liest oft Bücher the mother node (= the CP), the ↓-arrow to the fstructure of the node itself (= NP, C ).
2 the above rule states that CP dominates an NP and a C node; the NP functions as the subject (SUBJ) of CP, and C is the head of CP (sharing all features, by unification of their respective fstructures).