⊦ r0 ∈ st[r -- sk, val] .refs ↔ r0 = r ∨ r0 ∈ st .refs
[[CONCRETESIMPRULES : ([CSIMPSEQ : ⊦ r ∈ rset ++ r0 ↔ r = r0 ∨ r ∈ rset])]]