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<b>let </b><font color="Maroon">f</font> be   <a href="funct_1.html#NM1">Function</a>;<br/><b>let </b><font color="Maroon">g</font> be   <a href="funct_1.html#NM1">Function</a>;<br/><b>let </b><font color="Maroon">h</font> be   <a href="funct_1.html#NM1">Function</a>;<br/>





<a NAME="E1:15"/>
( <font color="Maroon">f</font> <a href="xboole_0.html#K3">/\</a> <font color="Maroon">g</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">f</font> &amp; <font color="Maroon">f</font> <a href="xboole_0.html#K3">/\</a> <font color="Maroon">g</font> <a href="tarski.html#R1">c=</a> <font color="Maroon">g</font> &amp; <font color="Maroon">f</font> <a href="xboole_0.html#K3">/\</a> <font color="Maroon">g</font> is   <a href="funct_1.html#NM1">Function</a> )
 
<b>by </b><i>, <a class="ref" href="xboole_1.html#T17">XBOOLE_1:17</a></i>;<br/>
<b>hence </b><a NAME="E2:15"/>
( ( <font color="Maroon">f</font> is <a href="funct_1.html#V2">one-to-one</a> or <font color="Maroon">g</font> is <a href="funct_1.html#V2">one-to-one</a> ) &amp; <font color="Maroon">h</font> <a href="hidden.html#R1">=</a> <font color="Maroon">f</font> <a href="xboole_0.html#K3">/\</a> <font color="Maroon">g</font> implies <font color="Maroon">h</font> is <a href="funct_1.html#V2">one-to-one</a> )
 <b>by </b><i/>;<br/>


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