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<b>let </b><font color="Maroon">x</font> be   <a href="supinf_1.html#NM3">R_eal</a>, <font color="Maroon">y</font> be   <a href="supinf_1.html#NM3">R_eal</a>;<br/>

<a NAME="E1:2"/>
( <font color="Maroon">x</font> <a href="supinf_2.html#K4">-</a> <font color="Maroon">y</font> <a href="xxreal_0.html#R1">&lt;=</a> <span class="p1"><a href="extreal1.html#K4">|.</a><span class="default"><span class="p2">(<span class="default"><font color="Maroon">x</font> <a href="supinf_2.html#K4">-</a> <font color="Maroon">y</font></span>)</span></span><a href="extreal1.html#K4">.|</a></span> &amp;  <a href="supinf_2.html#K3">-</a> <span class="p1"><a href="extreal1.html#K4">|.</a><span class="default"><span class="p2">(<span class="default"><font color="Maroon">x</font> <a href="supinf_2.html#K4">-</a> <font color="Maroon">y</font></span>)</span></span><a href="extreal1.html#K4">.|</a></span> <a href="xxreal_0.html#R1">&lt;=</a> <font color="Maroon">x</font> <a href="supinf_2.html#K4">-</a> <font color="Maroon">y</font> )
 
<b>by </b><i><a class="ref" href="extreal2.html#T57">EXTREAL2:57</a></i>;<br/>
<a NAME="E2:2"/><b>then </b>
( <font color="Maroon">x</font> <a href="supinf_2.html#K4">-</a> <font color="Maroon">y</font> <a href="xxreal_0.html#R1">&lt;=</a> <span class="p1"><a href="extreal1.html#K4">|.</a><span class="default"><span class="p2">(<span class="default"><font color="Maroon">x</font> <a href="supinf_2.html#K4">-</a> <font color="Maroon">y</font></span>)</span></span><a href="extreal1.html#K4">.|</a></span> &amp;  <a href="supinf_2.html#K3">-</a> <span class="p1">(<span class="default"><font color="Maroon">x</font> <a href="supinf_2.html#K4">-</a> <font color="Maroon">y</font></span>)</span> <a href="xxreal_0.html#R1">&lt;=</a> <span class="p1"><a href="extreal1.html#K4">|.</a><span class="default"><span class="p2">(<span class="default"><font color="Maroon">x</font> <a href="supinf_2.html#K4">-</a> <font color="Maroon">y</font></span>)</span></span><a href="extreal1.html#K4">.|</a></span> )
 
<b>by </b><i><a class="ref" href="extreal2.html#T47">EXTREAL2:47</a></i>;<br/>
<b>hence </b><a NAME="E3:2"/>
<font color="Maroon">y</font> <a href="supinf_2.html#K4">-</a> <font color="Maroon">x</font> <a href="xxreal_0.html#R1">&lt;=</a> <span class="p1"><a href="extreal1.html#K4">|.</a><span class="default"><span class="p2">(<span class="default"><font color="Maroon">x</font> <a href="supinf_2.html#K4">-</a> <font color="Maroon">y</font></span>)</span></span><a href="extreal1.html#K4">.|</a></span>
 <b>by </b><i><a class="ref" href="extreal2.html#T15">EXTREAL2:15</a></i>;<br/>


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