Define a grammar by setting σ = {σ} and let f consist of the following instruction formulas.
1. σ → n v.
2. n → n, for some n is in {he, she, josé, sal, anna}.
3. v → v, for some v is in {runs, jumps, skips, falls, swims}.
4. σ → σ p σ.
5. p → p, for some p is in {and, while until}.
6. σ → either σ or σ.