⊦ fid ∈ ofh.fids ↔ (∃ n. n ∈ ofh ∧ ofh[n].fid = fid)
⊦ (∃ n. n ∈ abs-of(of) ∧ abs-of(of)[n].fid = ⌜ino⌝ ) ↔ is-open(ino, of)
Used terms: abs-of(of), ⌜ino⌝