| h0 ⊥ h1, h2 ⊥ h3, h2 ⊥ h4, h3 ⊥ h4 ⊦ h0 ∪ h1 = h2 ∪ h3 ∪ h4 ↔ (∃ h20, h21, h30, h31, h40, h41. h2 = h20 ∪ h21 ∧ h3 = h30 ∪ h31 ∧ h4 = h40 ∪ h41 ∧ h0 = h20 ∪ h30 ∪ h40 ∧ h1 = h21 ∪ h31 ∪ h41 ∧ h20 ⊥ h21 ∧ h30 ⊥ h31 ∧ h40 ⊥ h41 ∧ h20 ⊥ h1 ∧ h30 ⊥ h1 ∧ h40 ⊥ h1 ∧ h21 ⊥ h0 ∧ h31 ⊥ h0 ∧ h41 ⊥ h0) |