ebm-cons(avols), v ∈ avols, ⌊err0⌋ ∨ err0 = ESUCCESS ⊦ ⟪err := err0⟫ true
ebm-cons(avols), v ∈ avols ⊦ ∃ err0. ⌊err0⌋ ∨ err0 = ESUCCESS