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<b>let </b><font color="Maroon">X</font> be    <a href="hidden.html#M1">set</a> , <font color="Maroon">Y</font> be    <a href="hidden.html#M1">set</a> ;<br/><b>let </b><font color="Maroon">f</font> be   <a href="funct_1.html#NM1">Function</a>;<br/>



<a NAME="E1:20"/>
( <font color="Maroon">X</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">X</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">Y</font> &amp; <font color="Maroon">Y</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">X</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">Y</font> )
 
<b>by </b><i><a class="ref" href="xboole_1.html#T7">XBOOLE_1:7</a></i>;<br/>
<a NAME="E2:20"/><b>then </b>
( <font color="Maroon">X</font> <a href="algspec1.html#K1" target="_self">-indexing</a> <font color="Maroon">f</font> <a href="hidden.html#R1">=</a> <span class="p1">(<span class="default"><span class="p2">(<span class="default"><font color="Maroon">X</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">Y</font></span>)</span> <a href="algspec1.html#K1" target="_self">-indexing</a> <font color="Maroon">f</font></span>)</span> <a href="relat_1.html#K7">|</a> <font color="Maroon">X</font> &amp; <font color="Maroon">Y</font> <a href="algspec1.html#K1" target="_self">-indexing</a> <font color="Maroon">f</font> <a href="hidden.html#R1">=</a> <span class="p1">(<span class="default"><span class="p2">(<span class="default"><font color="Maroon">X</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">Y</font></span>)</span> <a href="algspec1.html#K1" target="_self">-indexing</a> <font color="Maroon">f</font></span>)</span> <a href="relat_1.html#K7">|</a> <font color="Maroon">Y</font> )
 
<b>by </b><i/>;<br/>
<a NAME="E3:20"/><b>then </b>
( <font color="Maroon">X</font> <a href="algspec1.html#K1" target="_self">-indexing</a> <font color="Maroon">f</font> <a href="tarski.html#R1">c=</a> <span class="p1">(<span class="default"><font color="Maroon">X</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">Y</font></span>)</span> <a href="algspec1.html#K1" target="_self">-indexing</a> <font color="Maroon">f</font> &amp; <font color="Maroon">Y</font> <a href="algspec1.html#K1" target="_self">-indexing</a> <font color="Maroon">f</font> <a href="tarski.html#R1">c=</a> <span class="p1">(<span class="default"><font color="Maroon">X</font> <a href="xboole_0.html#K2">\/</a> <font color="Maroon">Y</font></span>)</span> <a href="algspec1.html#K1" target="_self">-indexing</a> <font color="Maroon">f</font> )
 
<b>by </b><i><a class="ref" href="relat_1.html#T88">RELAT_1:88</a></i>;<br/>
<b>hence </b><a NAME="E4:20"/>
<font color="Maroon">X</font> <a href="algspec1.html#K1" target="_self">-indexing</a> <font color="Maroon">f</font> <a href="partfun1.html#R1">tolerates</a> <font color="Maroon">Y</font> <a href="algspec1.html#K1" target="_self">-indexing</a> <font color="Maroon">f</font>
 <b>by </b><i><a class="ref" href="partfun1.html#T131">PARTFUN1:131</a></i>;<br/>


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