⌜x⌝ + ⌜nf⌝ = ⌜x⌝ + ⌜nf0⌝ ⊦ nf = nf0
Used simplifier rules: inj-01: ⊦ ⌜nf⌝ = ⌜nf0⌝ ↔ nf = nf0; from specification stream-basic