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<b>let </b><font color="Maroon">f1</font> be   <a href="partfun1.html#NM1">PartFunc</a> of the <a href="incsp_1.html#U1">Points</a> of <font color="Maroon">IPP</font>,the <a href="incsp_1.html#U1">Points</a> of <font color="Maroon">IPP</font>, <font color="Maroon">f2</font> be   <a href="partfun1.html#NM1">PartFunc</a> of the <a href="incsp_1.html#U1">Points</a> of <font color="Maroon">IPP</font>,the <a href="incsp_1.html#U1">Points</a> of <font color="Maroon">IPP</font>;<br/>

<b>assume </b><b>that </b><br/><a NAME="E1:20_1_2"/><i><font color="Green">E71</font></i>: 
(  <a href="relset_1.html#K4">dom</a> <font color="Maroon">f1</font> <a href="tarski.html#R1">c=</a> the <a href="incsp_1.html#U1">Points</a> of <font color="Maroon">IPP</font> &amp; ( for <font color="Olive">x</font> being  <a href="incsp_1.html#NM1">POINT</a> of <font color="Maroon">IPP</font> holds <br/> ( <font color="Olive">x</font> <a href="hidden.html#R2">in</a>  <a href="relset_1.html#K4">dom</a> <font color="Maroon">f1</font> iff <font color="Olive">x</font> <a href="incsp_1.html#R1">on</a> <font color="Maroon">K</font> ) ) )
 <b>and </b><br/><a NAME="E2:20_1_2"/><i><font color="Green">E72</font></i>: 
for <font color="Olive">x</font>, <font color="Olive">y</font> being  <a href="incsp_1.html#NM1">POINT</a> of <font color="Maroon">IPP</font>  st <font color="Olive">x</font> <a href="incsp_1.html#R1">on</a> <font color="Maroon">K</font> &amp; <font color="Olive">y</font> <a href="incsp_1.html#R1">on</a> <font color="Maroon">L</font> holds <br/>( <font color="Maroon">f1</font> <a href="funct_1.html#K1">.</a> <font color="Olive">x</font> <a href="hidden.html#R1">=</a> <font color="Olive">y</font> iff  ex <font color="Olive">X</font> being  <a href="incsp_1.html#NM2">LINE</a> of <font color="Maroon">IPP</font> st <br/>( <font color="Maroon">p</font> <a href="incsp_1.html#R1">on</a> <font color="Olive">X</font> &amp; <font color="Olive">x</font> <a href="incsp_1.html#R1">on</a> <font color="Olive">X</font> &amp; <font color="Olive">y</font> <a href="incsp_1.html#R1">on</a> <font color="Olive">X</font> ) )
 <b>and </b><br/><a NAME="E3:20_1_2"/><i><font color="Green">E73</font></i>: 
(  <a href="relset_1.html#K4">dom</a> <font color="Maroon">f2</font> <a href="tarski.html#R1">c=</a> the <a href="incsp_1.html#U1">Points</a> of <font color="Maroon">IPP</font> &amp; ( for <font color="Olive">x</font> being  <a href="incsp_1.html#NM1">POINT</a> of <font color="Maroon">IPP</font> holds <br/> ( <font color="Olive">x</font> <a href="hidden.html#R2">in</a>  <a href="relset_1.html#K4">dom</a> <font color="Maroon">f2</font> iff <font color="Olive">x</font> <a href="incsp_1.html#R1">on</a> <font color="Maroon">K</font> ) ) )
 <b>and </b><br/><a NAME="E4:20_1_2"/><i><font color="Green">E74</font></i>: 
for <font color="Olive">x</font>, <font color="Olive">y</font> being  <a href="incsp_1.html#NM1">POINT</a> of <font color="Maroon">IPP</font>  st <font color="Olive">x</font> <a href="incsp_1.html#R1">on</a> <font color="Maroon">K</font> &amp; <font color="Olive">y</font> <a href="incsp_1.html#R1">on</a> <font color="Maroon">L</font> holds <br/>( <font color="Maroon">f2</font> <a href="funct_1.html#K1">.</a> <font color="Olive">x</font> <a href="hidden.html#R1">=</a> <font color="Olive">y</font> iff  ex <font color="Olive">X</font> being  <a href="incsp_1.html#NM2">LINE</a> of <font color="Maroon">IPP</font> st <br/>( <font color="Maroon">p</font> <a href="incsp_1.html#R1">on</a> <font color="Olive">X</font> &amp; <font color="Olive">x</font> <a href="incsp_1.html#R1">on</a> <font color="Olive">X</font> &amp; <font color="Olive">y</font> <a href="incsp_1.html#R1">on</a> <font color="Olive">X</font> ) )
 ;<br/>

<a NAME="E5:20_1_2"/>
for <font color="Olive">x</font> being   <a href="hidden.html#M1">set</a>  holds <br/> ( <font color="Olive">x</font> <a href="hidden.html#R2">in</a>  <a href="relset_1.html#K4">dom</a> <font color="Maroon">f1</font> iff <font color="Olive">x</font> <a href="hidden.html#R2">in</a>  <a href="relset_1.html#K4">dom</a> <font color="Maroon">f2</font> )
 
<div><a class="txt" onclick="hs2(this)" href="javascript:()" title="20_1_2_1"><b>proof </b></a><div class="add">

<b>let </b><font color="Maroon">x</font> be    <a href="hidden.html#M1">set</a> ;<br/>

<a NAME="E1:20_1_2_1"/><i><font color="Green">E75</font></i>: 
( <font color="Maroon">x</font> <a href="hidden.html#R2">in</a>  <a href="relset_1.html#K4">dom</a> <font color="Maroon">f1</font> implies <font color="Maroon">x</font> <a href="hidden.html#R2">in</a>  <a href="relset_1.html#K4">dom</a> <font color="Maroon">f2</font> )
 
<div><a class="txt" onclick="hs2(this)" href="javascript:()" title="20_1_2_1_1"><b>proof </b></a><div class="add">

<b>assume </b><a NAME="E1:20_1_2_1_1"/><i><font color="Green">E76</font></i>: 
<font color="Maroon">x</font> <a href="hidden.html#R2">in</a>  <a href="relset_1.html#K4">dom</a> <font color="Maroon">f1</font>
 ;<br/>

<b>then reconsider </b><font color="Maroon">x</font> = <font color="Maroon">x</font> as    <a href="subset_1.html#M1">Element</a> of the <a href="incsp_1.html#U1">Points</a> of <font color="Maroon">IPP</font> ;<br/>
<a NAME="E3:20_1_2_1_1"/>
<font color="Maroon">x</font> <a href="incsp_1.html#R1">on</a> <font color="Maroon">K</font>
 
<b>by </b><i>, </i>;<br/>
<b>hence </b><a NAME="E4:20_1_2_1_1"/>
<font color="Maroon">x</font> <a href="hidden.html#R2">in</a>  <a href="relset_1.html#K4">dom</a> <font color="Maroon">f2</font>
 <b>by </b><i/>;<br/>


</div><b>end;</b></div>
<a NAME="E2:20_1_2_1"/>
( <font color="Maroon">x</font> <a href="hidden.html#R2">in</a>  <a href="relset_1.html#K4">dom</a> <font color="Maroon">f2</font> implies <font color="Maroon">x</font> <a href="hidden.html#R2">in</a>  <a href="relset_1.html#K4">dom</a> <font color="Maroon">f1</font> )
 
<div><a class="txt" onclick="hs2(this)" href="javascript:()" title="20_1_2_1_2"><b>proof </b></a><div class="add">

<b>assume </b><a NAME="E1:20_1_2_1_2"/><i><font color="Green">E77</font></i>: 
<font color="Maroon">x</font> <a href="hidden.html#R2">in</a>  <a href="relset_1.html#K4">dom</a> <font color="Maroon">f2</font>
 ;<br/>

<b>then reconsider </b><font color="Maroon">x</font> = <font color="Maroon">x</font> as    <a href="subset_1.html#M1">Element</a> of the <a href="incsp_1.html#U1">Points</a> of <font color="Maroon">IPP</font> ;<br/>
<a NAME="E3:20_1_2_1_2"/>
<font color="Maroon">x</font> <a href="incsp_1.html#R1">on</a> <font color="Maroon">K</font>
 
<b>by </b><i>, </i>;<br/>
<b>hence </b><a NAME="E4:20_1_2_1_2"/>
<font color="Maroon">x</font> <a href="hidden.html#R2">in</a>  <a href="relset_1.html#K4">dom</a> <font color="Maroon">f1</font>
 <b>by </b><i/>;<br/>


</div><b>end;</b></div>
<b>hence </b><a NAME="E3:20_1_2_1"/>
( <font color="Maroon">x</font> <a href="hidden.html#R2">in</a>  <a href="relset_1.html#K4">dom</a> <font color="Maroon">f1</font> iff <font color="Maroon">x</font> <a href="hidden.html#R2">in</a>  <a href="relset_1.html#K4">dom</a> <font color="Maroon">f2</font> )
 <b>by </b><i/>;<br/>


</div><b>end;</b></div>
<a NAME="E6:20_1_2"/><b>then </b><i><font color="Green">E78</font></i>: 
 <a href="relset_1.html#K4">dom</a> <font color="Maroon">f1</font> <a href="hidden.html#R1">=</a>  <a href="relset_1.html#K4">dom</a> <font color="Maroon">f2</font>
 
<b>by </b><i><a class="ref" href="tarski.html#T2">TARSKI:2</a></i>;<br/>
<a NAME="E7:20_1_2"/>
for <font color="Olive">x</font> being  <a href="incsp_1.html#NM1">POINT</a> of <font color="Maroon">IPP</font>  st <font color="Olive">x</font> <a href="hidden.html#R2">in</a>  <a href="relset_1.html#K4">dom</a> <font color="Maroon">f1</font> holds <br/><font color="Maroon">f1</font> <a href="funct_1.html#K1">.</a> <font color="Olive">x</font> <a href="hidden.html#R1">=</a> <font color="Maroon">f2</font> <a href="funct_1.html#K1">.</a> <font color="Olive">x</font>
 
<div><a class="txt" onclick="hs2(this)" href="javascript:()" title="20_1_2_2"><b>proof </b></a><div class="add">

<b>let </b><font color="Maroon">x</font> be   <a href="incsp_1.html#NM1">POINT</a> of <font color="Maroon">IPP</font>;<br/>

<b>assume </b><a NAME="E1:20_1_2_2"/>
<font color="Maroon">x</font> <a href="hidden.html#R2">in</a>  <a href="relset_1.html#K4">dom</a> <font color="Maroon">f1</font>
 ;<br/>

<a NAME="E2:20_1_2_2"/><b>then </b><i><font color="Green">E79</font></i>: 
<font color="Maroon">x</font> <a href="incsp_1.html#R1">on</a> <font color="Maroon">K</font>
 
<b>by </b><i/>;<br/>
<b>consider </b><font color="Maroon">A2</font> being   <a href="incsp_1.html#NM2">LINE</a> of <font color="Maroon">IPP</font><b> such that </b><br/><a NAME="E4:20_1_2_2"/><i><font color="Green">E80</font></i>: 
( <font color="Maroon">p</font> <a href="incsp_1.html#R1">on</a> <font color="Maroon">A2</font> &amp; <font color="Maroon">x</font> <a href="incsp_1.html#R1">on</a> <font color="Maroon">A2</font> )
 <b>by </b><i><a class="ref" href="incproj.html#D10">INCPROJ:def 10</a></i>;<br/>
<b>consider </b><font color="Maroon">y2</font> being   <a href="incsp_1.html#NM1">POINT</a> of <font color="Maroon">IPP</font><b> such that </b><br/><a NAME="E6:20_1_2_2"/><i><font color="Green">E81</font></i>: 
( <font color="Maroon">y2</font> <a href="incsp_1.html#R1">on</a> <font color="Maroon">A2</font> &amp; <font color="Maroon">y2</font> <a href="incsp_1.html#R1">on</a> <font color="Maroon">L</font> )
 <b>by </b><i><a class="ref" href="incproj.html#D14">INCPROJ:def 14</a></i>;<br/>
<a NAME="E7:20_1_2_2"/>
<font color="Maroon">f2</font> <a href="funct_1.html#K1">.</a> <font color="Maroon">x</font> <a href="hidden.html#R1">=</a> <font color="Maroon">y2</font>
 
<b>by </b><i>, , , </i>;<br/>
<b>hence </b><a NAME="E8:20_1_2_2"/>
<font color="Maroon">f1</font> <a href="funct_1.html#K1">.</a> <font color="Maroon">x</font> <a href="hidden.html#R1">=</a> <font color="Maroon">f2</font> <a href="funct_1.html#K1">.</a> <font color="Maroon">x</font>
 <b>by </b><i>, , , </i>;<br/>


</div><b>end;</b></div>
<b>hence </b><a NAME="E8:20_1_2"/>
<font color="Maroon">f1</font> <a href="hidden.html#R1">=</a> <font color="Maroon">f2</font>
 <b>by </b><i>, <a class="ref" href="partfun1.html#T34">PARTFUN1:34</a></i>;<br/>


</div>
