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<span class="kw">let </span><font color="Maroon" title="c4">x1</font>, <font color="Maroon" title="c5">x2</font> be    <a href="finseq_2.html#M2" title="FINSEQ_2:mode.2">Element</a> of  <a href="euclid.html#K1" title="EUCLID:func.1">REAL</a> <font color="Maroon" title="c1">n</font>; <a class="txt" onclick="hs(this)" href="javascript:()"><span class="comment"><font color="firebrick">::  thesis: </font></span></a><span class="hide">  <a href="euclid_4.html#K1" title="EUCLID_4:func.1">Line</a> (<font color="Maroon" title="c4">x1</font>,<font color="Maroon" title="c5">x2</font>) <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a>  <a href="euclid_4.html#K1" title="EUCLID_4:func.1">Line</a> (<font color="Maroon" title="c5">x2</font>,<font color="Maroon" title="c4">x1</font>)</span><br/>



<a NAME="E1:9_1_1"/>
(  <a href="euclid_4.html#K1" title="EUCLID_4:func.1">Line</a> (<font color="Maroon" title="c4">x1</font>,<font color="Maroon" title="c5">x2</font>) <a href="tarski.html#R1" title="TARSKI:pred.1">c=</a>  <a href="euclid_4.html#K1" title="EUCLID_4:func.1">Line</a> (<font color="Maroon" title="c5">x2</font>,<font color="Maroon" title="c4">x1</font>) &amp;  <a href="euclid_4.html#K1" title="EUCLID_4:func.1">Line</a> (<font color="Maroon" title="c5">x2</font>,<font color="Maroon" title="c4">x1</font>) <a href="tarski.html#R1" title="TARSKI:pred.1">c=</a>  <a href="euclid_4.html#K1" title="EUCLID_4:func.1">Line</a> (<font color="Maroon" title="c4">x1</font>,<font color="Maroon" title="c5">x2</font>) )
 
<span class="kw">by</span> <span class="lab"><a class="txt" href="euclid_4.html#E10"><span class="lab"><font color="Green" title="E4">Lm1</font></span></a></span>;<br/>
<span class="kw">hence </span><a NAME="E2:9_1_1"/>
 <a href="euclid_4.html#K1" title="EUCLID_4:func.1">Line</a> (<font color="Maroon" title="c4">x1</font>,<font color="Maroon" title="c5">x2</font>) <a href="hidden.html#R1" title="HIDDEN:pred.1">=</a>  <a href="euclid_4.html#K1" title="EUCLID_4:func.1">Line</a> (<font color="Maroon" title="c5">x2</font>,<font color="Maroon" title="c4">x1</font>)
 <span class="kw">by</span> <span class="lab"><a class="ref" href="xboole_0.html#D10" title="XBOOLE_0:def.10">XBOOLE_0:def 10</a></span>; <a class="txt" onclick="hs(this)" href="javascript:()"><span class="comment"><font color="firebrick">::  thesis: </font></span></a><span class="hide"> verum</span><br/>


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