⊦ lls(r0, r2, x + a ')(H) ↔ (∃ r. (lls(r0, r, x) * r => a × r2)(H))
[[CONCRETESIMPRULES : ([CSIMPSEQ : ⊦ (_∃ rP)(H) ↔ (∃ r. rP(r)(H))])]]