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<b>let </b><font color="Maroon">n</font> be    <a href="subset_1.html#M1">Element</a> of  <a href="numbers.html#K5">NAT</a> ;<br/><b>let </b><font color="Maroon">x1</font> be    <a href="subset_1.html#M1">Element</a> of  <a href="euclid.html#K1">REAL</a> <font color="Maroon">n</font>;<br/><b>let </b><font color="Maroon">x2</font> be    <a href="subset_1.html#M1">Element</a> of  <a href="euclid.html#K1">REAL</a> <font color="Maroon">n</font>;<br/>





<a NAME="E1:12"/>
(  <a href="euclid_4.html#K1" target="_self">Line</a> <font color="Maroon">x1</font>,<font color="Maroon">x2</font> <a href="tarski.html#R1">c=</a>  <a href="euclid_4.html#K1" target="_self">Line</a> <font color="Maroon">x2</font>,<font color="Maroon">x1</font> &amp;  <a href="euclid_4.html#K1" target="_self">Line</a> <font color="Maroon">x2</font>,<font color="Maroon">x1</font> <a href="tarski.html#R1">c=</a>  <a href="euclid_4.html#K1" target="_self">Line</a> <font color="Maroon">x1</font>,<font color="Maroon">x2</font> )
 
<b>by </b><i/>;<br/>
<b>hence </b><a NAME="E2:12"/>
 <a href="euclid_4.html#K1" target="_self">Line</a> <font color="Maroon">x1</font>,<font color="Maroon">x2</font> <a href="hidden.html#R1">=</a>  <a href="euclid_4.html#K1" target="_self">Line</a> <font color="Maroon">x2</font>,<font color="Maroon">x1</font>
 <b>by </b><i><a class="ref" href="xboole_0.html#D10">XBOOLE_0:def 10</a></i>;<br/>


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