#8221;).</p>
<p style="text-align: justify;">In the IFF, the operations of
contraction, expansion and revision are not primitive. Suppose we have
a theory <span style="font-style: italic; font-weight: bold;">T</span>
= (<span style="font-family: arial; font-style: italic;">base</span>(<span
 style="font-style: italic; font-weight: bold;">T</span>), <span
 style="font-family: arial; font-style: italic;">axm</span>(<span
 style="font-weight: bold; font-style: italic;">T</span>)) over a base
type language
<spa