: <span
 style="font-family: arial; font-style: italic;">entail</span>(<span
 style="font-weight: bold; font-style: italic;">L</span>) &middot; <span
 style="font-family: arial; font-style: italic;">right</span>(<span
 style="font-weight: bold; font-style: italic;">f</span>)
= <span style="font-family: arial; font-style: italic;">expr</span>(<span
 style="font-weight: bold; font-style: italic;">f</span>) &middot; <span
 style="font-family: arial; font-style: italic;">entail</span>(<span
 style="font-style: 