⊦ ofh = ofh0 ↔ (∀ fd. (fd ∈ ofh ↔ fd ∈ ofh0) ∧ ofh[fd] = ofh0[fd])
⊦ ∀ fd. (fd ∈ abs-of(∅) ↔ fd ∈ ∅) ∧ abs-of(∅)[fd] = (∅)[fd]
Used terms: ∅, abs-of(∅)