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<div>:: <span class="kw">deftheorem </span>   defines <a href="prob_1.html#K12" title="PROB_1:func.12">Borel_Sets</a> <a onclick="hs(this)" href="javascript:()">PROB_1:def 12 : <br/></a><span> <a href="prob_1.html#K12" title="PROB_1:func.12">Borel_Sets</a>  <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a>  <a href="prob_1.html#K9" title="PROB_1:func.9">sigma</a> <a href="prob_1.html#K11" title="PROB_1:func.11">Family_of_halflines</a>;<br/></span></div>
