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<code class="code"><span class="constructor">Hashtbl</span>.add&nbsp;tbl&nbsp;x&nbsp;y</code> adds a binding of <code class="code">x</code> to <code class="code">y</code> in table <code class="code">tbl</code>.
   Previous bindings for <code class="code">x</code> are not removed, but simply
   hidden. That is, after performing <a href="Hashtbl.html#VALremove"><code class="code"><span class="constructor">Hashtbl</span>.remove</code></a><code class="code">&nbsp;tbl&nbsp;x</code>,
   the previous binding