/span></big><span
 style="font-family: arial; font-style: italic;">expr</span>(<span
 style="font-style: italic; font-weight: bold;">L</span>) &#8594; <big><span
 style="font-family: script mt bold;">P</span></big><span
 style="font-family: arial; font-style: italic;">expr</span>(<span
 style="font-style: italic; font-weight: bold;">&#321;</span>) on the
theorem
sets, and the closure function <span
 style="font-family: arial; font-style: italic;">clo</span>(<span
 style="font-style: italic; font-weight: bol