<?xml version="1.0"?>
<div class="add">

<b>set </b><font color="Maroon">c<sub>1</sub></font> = <span class="p1"><a href="tarski.html#K2">{</a><span class="default">1,2</span><a href="tarski.html#K2">}</a></span>;<br/>
<b>set </b><font color="Maroon">c<sub>2</sub></font> = <span class="p1"><a href="tarski.html#K1">{</a><span class="default">1</span><a href="tarski.html#K1">}</a></span>;<br/>
<a NAME="E1:9_1_1"/><i><font color="Green">E5</font></i>: 
1 <a href="hidden.html#R2">in</a> <span class="p1"><a href="tarski.html#K1">{</a><span class="default">1</span><a href="tarski.html#K1">}</a></span>
 
<b>by </b><i><a class="ref" href="tarski.html#D1">TARSKI:def 1</a></i>;<br/>
<a NAME="E2:9_1_1"/>
( 1 <a href="hidden.html#R2">in</a> <span class="p1"><a href="tarski.html#K2">{</a><span class="default">1,2</span><a href="tarski.html#K2">}</a></span> &amp; 2 <a href="hidden.html#R2">in</a> <span class="p1"><a href="tarski.html#K2">{</a><span class="default">1,2</span><a href="tarski.html#K2">}</a></span> )
 
<b>by </b><i><a class="ref" href="tarski.html#D2">TARSKI:def 2</a></i>;<br/>
<b>then reconsider </b><font color="Maroon">c<sub>3</sub></font> = <span class="p1"><a href="tarski.html#K1">{</a><span class="default">1</span><a href="tarski.html#K1">}</a></span> <a href="pre_circ.html#K2">--&gt;</a> 1, <font color="Maroon">c<sub>4</sub></font> = <span class="p1"><a href="tarski.html#K1">{</a><span class="default">1</span><a href="tarski.html#K1">}</a></span> <a href="pre_circ.html#K2">--&gt;</a> 2 as   <a href="funct_2.html#NM1">Function</a> of <span class="p1"><a href="tarski.html#K1">{</a><span class="default">1</span><a href="tarski.html#K1">}</a></span>,<span class="p1"><a href="tarski.html#K2">{</a><span class="default">1,2</span><a href="tarski.html#K2">}</a></span> <b>by </b><i><a class="ref" href="funcop_1.html#T57">FUNCOP_1:57</a></i>;<br/>
<b>reconsider </b><font color="Maroon">c<sub>5</sub></font> =  <a href="graph_1.html#G1">MultiGraphStruct</a>(# <span class="p1"><a href="tarski.html#K2">{</a><span class="default">1,2</span><a href="tarski.html#K2">}</a></span>,<span class="p1"><a href="tarski.html#K1">{</a><span class="default">1</span><a href="tarski.html#K1">}</a></span>,<font color="Maroon">c<sub>3</sub></font>,<font color="Maroon">c<sub>4</sub></font> #) as   <a href="graph_1.html#NM1">Graph</a> <b>by </b><i><a class="ref" href="graph_1.html#D1">GRAPH_1:def 1</a></i>;<br/>
<a NAME="E5:9_1_1"/><i><font color="Green">E6</font></i>: 
( <font color="Maroon">c<sub>3</sub></font> <a href="funct_1.html#K1">.</a> 1 <a href="hidden.html#R1">=</a> 1 &amp; <font color="Maroon">c<sub>4</sub></font> <a href="funct_1.html#K1">.</a> 1 <a href="hidden.html#R1">=</a> 2 )
 
<b>by </b><i><a class="txt" href="msscyc_1.html#E1:9_1_1"><i><font color="Green">E5</font></i></a>, <a class="ref" href="funcop_1.html#T13">FUNCOP_1:13</a></i>;<br/>
<b>take </b>
<font color="Maroon">c<sub>5</sub></font>
;<br/>

<b>thus </b><a NAME="E6:9_1_1"/>
<font color="Maroon">c<sub>5</sub></font> is <a href="graph_1.html#V7">finite</a>
 <b>by </b><i><a class="ref" href="graph_1.html#D8">GRAPH_1:def 8</a></i>;<br/>

<b>thus </b><a NAME="E7:9_1_1"/>
<font color="Maroon">c<sub>5</sub></font> is <a href="graph_1.html#V5">simple</a>
 <div><a class="txt" onclick="hs2(this)" href="javascript:()" title="9_1_1_1"><b>proof </b></a><div class="add">

<b>given </b><font color="Maroon">c<sub>6</sub></font> being    <a href="hidden.html#M1">set</a> <b> such that </b><a NAME="E1:9_1_1_1"/><i><font color="Green">E7</font></i>: 
( <font color="Maroon">c<sub>6</sub></font> <a href="hidden.html#R2">in</a> the <a href="graph_1.html#U2">Edges</a> of <font color="Maroon">c<sub>5</sub></font> &amp; the <a href="graph_1.html#U3">Source</a> of <font color="Maroon">c<sub>5</sub></font> <a href="funct_1.html#K1">.</a> <font color="Maroon">c<sub>6</sub></font> <a href="hidden.html#R1">=</a> the <a href="graph_1.html#U4">Target</a> of <font color="Maroon">c<sub>5</sub></font> <a href="funct_1.html#K1">.</a> <font color="Maroon">c<sub>6</sub></font> )
 ; <i><font color="Red">:: according to </font></i><a class="ref" href="graph_1.html#D6">GRAPH_1:def 6</a><br/>

<a NAME="E2:9_1_1_1"/>
<font color="Maroon">c<sub>6</sub></font> <a href="hidden.html#R1">=</a> 1
 
<b>by </b><i><a class="txt" href="msscyc_1.html#E1:9_1_1_1"><i><font color="Green">E7</font></i></a>, <a class="ref" href="tarski.html#D1">TARSKI:def 1</a></i>;<br/>
<b>hence </b><a NAME="E3:9_1_1_1"/>
contradiction
 <b>by </b><i><a class="txt" href="msscyc_1.html#E5:9_1_1"><i><font color="Green">E6</font></i></a>, <a class="txt" href="msscyc_1.html#E1:9_1_1_1"><i><font color="Green">E7</font></i></a></i>;<br/>


</div><b>end;</b></div>

<b>thus </b><a NAME="E8:9_1_1"/>
<font color="Maroon">c<sub>5</sub></font> is <a href="graph_1.html#V6">connected</a>
 <div><a class="txt" onclick="hs2(this)" href="javascript:()" title="9_1_1_2"><b>proof </b></a><div class="add">

<b>given </b><font color="Maroon">c<sub>6</sub></font>, <font color="Maroon">c<sub>7</sub></font> being   <a href="graph_1.html#NM1">Graph</a><b> such that </b><a NAME="E1:9_1_1_2"/><i><font color="Green">E7</font></i>: 
( the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>6</sub></font> <a href="subset_1.html#R1">misses</a> the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>7</sub></font> &amp; <font color="Maroon">c<sub>5</sub></font> <a href="graph_1.html#R1">is_sum_of</a> <font color="Maroon">c<sub>6</sub></font>,<font color="Maroon">c<sub>7</sub></font> )
 ; <i><font color="Red">:: according to </font></i><a class="ref" href="graph_1.html#D7">GRAPH_1:def 7</a><br/>

<b>set </b><font color="Maroon">c<sub>8</sub></font> =  <a href="graph_1.html#G1">MultiGraphStruct</a>(# the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>5</sub></font>,the <a href="graph_1.html#U2">Edges</a> of <font color="Maroon">c<sub>5</sub></font>,the <a href="graph_1.html#U3">Source</a> of <font color="Maroon">c<sub>5</sub></font>,the <a href="graph_1.html#U4">Target</a> of <font color="Maroon">c<sub>5</sub></font> #);<br/>
<a NAME="E2:9_1_1_2"/><i><font color="Green">E8</font></i>: 
( the <a href="graph_1.html#U4">Target</a> of <font color="Maroon">c<sub>6</sub></font> <a href="partfun1.html#R1">tolerates</a> the <a href="graph_1.html#U4">Target</a> of <font color="Maroon">c<sub>7</sub></font> &amp; the <a href="graph_1.html#U3">Source</a> of <font color="Maroon">c<sub>6</sub></font> <a href="partfun1.html#R1">tolerates</a> the <a href="graph_1.html#U3">Source</a> of <font color="Maroon">c<sub>7</sub></font> &amp;  <a href="graph_1.html#G1">MultiGraphStruct</a>(# the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>5</sub></font>,the <a href="graph_1.html#U2">Edges</a> of <font color="Maroon">c<sub>5</sub></font>,the <a href="graph_1.html#U3">Source</a> of <font color="Maroon">c<sub>5</sub></font>,the <a href="graph_1.html#U4">Target</a> of <font color="Maroon">c<sub>5</sub></font> #) <a href="hidden.html#R1">=</a> <font color="Maroon">c<sub>6</sub></font> <a href="graph_1.html#K1">\/</a> <font color="Maroon">c<sub>7</sub></font> )
 
<b>by </b><i><a class="txt" href="msscyc_1.html#E1:9_1_1_2"><i><font color="Green">E7</font></i></a>, <a class="ref" href="graph_1.html#D3">GRAPH_1:def 3</a></i>;<br/>
<a NAME="E3:9_1_1_2"/><b>then </b><i><font color="Green">E9</font></i>: 
( the <a href="graph_1.html#U1">Vertices</a> of <a href="graph_1.html#G1">MultiGraphStruct</a>(# the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>5</sub></font>,the <a href="graph_1.html#U2">Edges</a> of <font color="Maroon">c<sub>5</sub></font>,the <a href="graph_1.html#U3">Source</a> of <font color="Maroon">c<sub>5</sub></font>,the <a href="graph_1.html#U4">Target</a> of <font color="Maroon">c<sub>5</sub></font> #) <a href="hidden.html#R1">=</a> the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>6</sub></font> <a href="xboole_0.html#K2">\/</a> the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>7</sub></font> &amp; the <a href="graph_1.html#U2">Edges</a> of <a href="graph_1.html#G1">MultiGraphStruct</a>(# the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>5</sub></font>,the <a href="graph_1.html#U2">Edges</a> of <font color="Maroon">c<sub>5</sub></font>,the <a href="graph_1.html#U3">Source</a> of <font color="Maroon">c<sub>5</sub></font>,the <a href="graph_1.html#U4">Target</a> of <font color="Maroon">c<sub>5</sub></font> #) <a href="hidden.html#R1">=</a> the <a href="graph_1.html#U2">Edges</a> of <font color="Maroon">c<sub>6</sub></font> <a href="xboole_0.html#K2">\/</a> the <a href="graph_1.html#U2">Edges</a> of <font color="Maroon">c<sub>7</sub></font> )
 
<b>by </b><i><a class="ref" href="graph_1.html#D2">GRAPH_1:def 2</a></i>;<br/>
<b>set </b><font color="Maroon">c<sub>9</sub></font> = the <a href="graph_1.html#U2">Edges</a> of <font color="Maroon">c<sub>6</sub></font>;<br/>
<b>set </b><font color="Maroon">c<sub>10</sub></font> = the <a href="graph_1.html#U2">Edges</a> of <font color="Maroon">c<sub>7</sub></font>;<br/>
<b>set </b><font color="Maroon">c<sub>11</sub></font> = the <a href="graph_1.html#U3">Source</a> of <font color="Maroon">c<sub>6</sub></font>;<br/>
<b>set </b><font color="Maroon">c<sub>12</sub></font> = the <a href="graph_1.html#U3">Source</a> of <font color="Maroon">c<sub>7</sub></font>;<br/>
<b>set </b><font color="Maroon">c<sub>13</sub></font> = the <a href="graph_1.html#U4">Target</a> of <font color="Maroon">c<sub>6</sub></font>;<br/>
<b>set </b><font color="Maroon">c<sub>14</sub></font> = the <a href="graph_1.html#U4">Target</a> of <font color="Maroon">c<sub>7</sub></font>;<br/>
<b>set </b><font color="Maroon">c<sub>15</sub></font> = the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>6</sub></font>;<br/>
<b>set </b><font color="Maroon">c<sub>16</sub></font> = the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>7</sub></font>;<br/>
<a NAME="E4:9_1_1_2"/><i><font color="Green">E10</font></i>: 
<span class="p1">(<span class="default"><a href="relat_1.html#K2">rng</a> the <a href="graph_1.html#U3">Source</a> of <font color="Maroon">c<sub>6</sub></font></span>)</span> <a href="xboole_0.html#K2">\/</a> <span class="p1">(<span class="default"><a href="relat_1.html#K2">rng</a> the <a href="graph_1.html#U4">Target</a> of <font color="Maroon">c<sub>6</sub></font></span>)</span> <a href="tarski.html#R1">c=</a> the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>6</sub></font>
 
<b>by </b><i><a class="ref" href="msscyc_1.html#T3" target="_self">Th3</a></i>;<br/>
<a NAME="E5:9_1_1_2"/><i><font color="Green">E11</font></i>: 
<span class="p1">(<span class="default"><a href="relat_1.html#K2">rng</a> the <a href="graph_1.html#U3">Source</a> of <font color="Maroon">c<sub>7</sub></font></span>)</span> <a href="xboole_0.html#K2">\/</a> <span class="p1">(<span class="default"><a href="relat_1.html#K2">rng</a> the <a href="graph_1.html#U4">Target</a> of <font color="Maroon">c<sub>7</sub></font></span>)</span> <a href="tarski.html#R1">c=</a> the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>7</sub></font>
 
<b>by </b><i><a class="ref" href="msscyc_1.html#T3" target="_self">Th3</a></i>;<br/>
<div><a class="txt" onclick="hsNdiv(this)" href="javascript:()" title="9_1_1_2_1"><b>per </b></a><a class="txt" onclick="hs(this)" href="javascript:()"><b>cases </b></a><span class="hide"><a NAME="E1:9_1_1_2_1"/>
( ( the <a href="graph_1.html#U2">Edges</a> of <font color="Maroon">c<sub>6</sub></font> <a href="hidden.html#R1">=</a> <span class="p1"><a href="tarski.html#K1">{</a><span class="default">1</span><a href="tarski.html#K1">}</a></span> &amp; the <a href="graph_1.html#U2">Edges</a> of <font color="Maroon">c<sub>7</sub></font> <a href="hidden.html#R1">=</a> <span class="p1"><a href="tarski.html#K1">{</a><span class="default">1</span><a href="tarski.html#K1">}</a></span> ) or ( the <a href="graph_1.html#U2">Edges</a> of <font color="Maroon">c<sub>6</sub></font> <a href="hidden.html#R1">=</a> <span class="p1"><a href="tarski.html#K1">{</a><span class="default">1</span><a href="tarski.html#K1">}</a></span> &amp; the <a href="graph_1.html#U2">Edges</a> of <font color="Maroon">c<sub>7</sub></font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a>  ) or ( the <a href="graph_1.html#U2">Edges</a> of <font color="Maroon">c<sub>6</sub></font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a>  &amp; the <a href="graph_1.html#U2">Edges</a> of <font color="Maroon">c<sub>7</sub></font> <a href="hidden.html#R1">=</a> <span class="p1"><a href="tarski.html#K1">{</a><span class="default">1</span><a href="tarski.html#K1">}</a></span> ) )
 </span><b>by </b><i><a class="txt" href="msscyc_1.html#E3:9_1_1_2"><i><font color="Green">E9</font></i></a>, <a class="ref" href="zfmisc_1.html#T43">ZFMISC_1:43</a></i>;<br/><div class="add"><div><a class="txt" onclick="hsNdiv(this)" href="javascript:()" title="9_1_1_2_1_1"><b>suppose </b></a><a NAME="E1:9_1_1_2_1_1"/><i><font color="Green">E12</font></i>: 
( the <a href="graph_1.html#U2">Edges</a> of <font color="Maroon">c<sub>6</sub></font> <a href="hidden.html#R1">=</a> <span class="p1"><a href="tarski.html#K1">{</a><span class="default">1</span><a href="tarski.html#K1">}</a></span> &amp; the <a href="graph_1.html#U2">Edges</a> of <font color="Maroon">c<sub>7</sub></font> <a href="hidden.html#R1">=</a> <span class="p1"><a href="tarski.html#K1">{</a><span class="default">1</span><a href="tarski.html#K1">}</a></span> )
 ;<br/><div class="add"><a NAME="E2:9_1_1_2_1_1"/><b>then </b>
( the <a href="graph_1.html#U3">Source</a> of <font color="Maroon">c<sub>6</sub></font> <a href="funct_1.html#K1">.</a> 1 <a href="hidden.html#R1">=</a> <font color="Maroon">c<sub>3</sub></font> <a href="funct_1.html#K1">.</a> 1 &amp; the <a href="graph_1.html#U3">Source</a> of <font color="Maroon">c<sub>7</sub></font> <a href="funct_1.html#K1">.</a> 1 <a href="hidden.html#R1">=</a> <font color="Maroon">c<sub>3</sub></font> <a href="funct_1.html#K1">.</a> 1 )
 <b>by </b><i><a class="txt" href="msscyc_1.html#E1:9_1_1"><i><font color="Green">E5</font></i></a>, <a class="txt" href="msscyc_1.html#E2:9_1_1_2"><i><font color="Green">E8</font></i></a>, <a class="ref" href="graph_1.html#D2">GRAPH_1:def 2</a></i>;<br/><a NAME="E3:9_1_1_2_1_1"/><b>then </b>
( 1 <a href="hidden.html#R2">in</a>  <a href="relat_1.html#K2">rng</a> the <a href="graph_1.html#U3">Source</a> of <font color="Maroon">c<sub>6</sub></font> &amp; 1 <a href="hidden.html#R2">in</a>  <a href="relat_1.html#K2">rng</a> the <a href="graph_1.html#U3">Source</a> of <font color="Maroon">c<sub>7</sub></font> )
 <b>by </b><i><a class="txt" href="msscyc_1.html#E1:9_1_1"><i><font color="Green">E5</font></i></a>, <a class="txt" href="msscyc_1.html#E5:9_1_1"><i><font color="Green">E6</font></i></a>, <a class="txt" href="msscyc_1.html#E1:9_1_1_2_1_1"><i><font color="Green">E12</font></i></a>, <a class="ref" href="funct_2.html#T6">FUNCT_2:6</a></i>;<br/><a NAME="E4:9_1_1_2_1_1"/><b>then </b>
( 1 <a href="hidden.html#R2">in</a> <span class="p1">(<span class="default"><a href="relat_1.html#K2">rng</a> the <a href="graph_1.html#U3">Source</a> of <font color="Maroon">c<sub>6</sub></font></span>)</span> <a href="xboole_0.html#K2">\/</a> <span class="p1">(<span class="default"><a href="relat_1.html#K2">rng</a> the <a href="graph_1.html#U4">Target</a> of <font color="Maroon">c<sub>6</sub></font></span>)</span> &amp; 1 <a href="hidden.html#R2">in</a> <span class="p1">(<span class="default"><a href="relat_1.html#K2">rng</a> the <a href="graph_1.html#U3">Source</a> of <font color="Maroon">c<sub>7</sub></font></span>)</span> <a href="xboole_0.html#K2">\/</a> <span class="p1">(<span class="default"><a href="relat_1.html#K2">rng</a> the <a href="graph_1.html#U4">Target</a> of <font color="Maroon">c<sub>7</sub></font></span>)</span> )
 <b>by </b><i><a class="ref" href="xboole_0.html#D2">XBOOLE_0:def 2</a></i>;<br/><b>hence </b><a NAME="E5:9_1_1_2_1_1"/>
contradiction
 <b>by </b><i><a class="txt" href="msscyc_1.html#E1:9_1_1_2"><i><font color="Green">E7</font></i></a>, <a class="txt" href="msscyc_1.html#E4:9_1_1_2"><i><font color="Green">E10</font></i></a>, <a class="txt" href="msscyc_1.html#E5:9_1_1_2"><i><font color="Green">E11</font></i></a>, <a class="ref" href="xboole_0.html#T3">XBOOLE_0:3</a></i>;<br/></div><b>end;</b></div><div><a class="txt" onclick="hsNdiv(this)" href="javascript:()" title="9_1_1_2_1_2"><b>suppose </b></a><a NAME="E1:9_1_1_2_1_2"/><i><font color="Green">E12</font></i>: 
( the <a href="graph_1.html#U2">Edges</a> of <font color="Maroon">c<sub>6</sub></font> <a href="hidden.html#R1">=</a> <span class="p1"><a href="tarski.html#K1">{</a><span class="default">1</span><a href="tarski.html#K1">}</a></span> &amp; the <a href="graph_1.html#U2">Edges</a> of <font color="Maroon">c<sub>7</sub></font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a>  )
 ;<br/><div class="add"><a NAME="E2:9_1_1_2_1_2"/><b>then </b>
( the <a href="graph_1.html#U3">Source</a> of <font color="Maroon">c<sub>6</sub></font> <a href="funct_1.html#K1">.</a> 1 <a href="hidden.html#R1">=</a> <font color="Maroon">c<sub>3</sub></font> <a href="funct_1.html#K1">.</a> 1 &amp; the <a href="graph_1.html#U4">Target</a> of <font color="Maroon">c<sub>6</sub></font> <a href="funct_1.html#K1">.</a> 1 <a href="hidden.html#R1">=</a> <font color="Maroon">c<sub>4</sub></font> <a href="funct_1.html#K1">.</a> 1 )
 <b>by </b><i><a class="txt" href="msscyc_1.html#E1:9_1_1"><i><font color="Green">E5</font></i></a>, <a class="txt" href="msscyc_1.html#E2:9_1_1_2"><i><font color="Green">E8</font></i></a>, <a class="ref" href="graph_1.html#D2">GRAPH_1:def 2</a></i>;<br/><a NAME="E3:9_1_1_2_1_2"/><b>then </b>
( 1 <a href="hidden.html#R2">in</a>  <a href="relat_1.html#K2">rng</a> the <a href="graph_1.html#U3">Source</a> of <font color="Maroon">c<sub>6</sub></font> &amp; 2 <a href="hidden.html#R2">in</a>  <a href="relat_1.html#K2">rng</a> the <a href="graph_1.html#U4">Target</a> of <font color="Maroon">c<sub>6</sub></font> )
 <b>by </b><i><a class="txt" href="msscyc_1.html#E1:9_1_1"><i><font color="Green">E5</font></i></a>, <a class="txt" href="msscyc_1.html#E5:9_1_1"><i><font color="Green">E6</font></i></a>, <a class="txt" href="msscyc_1.html#E1:9_1_1_2_1_2"><i><font color="Green">E12</font></i></a>, <a class="ref" href="funct_2.html#T6">FUNCT_2:6</a></i>;<br/><a NAME="E4:9_1_1_2_1_2"/><b>then </b>
( 1 <a href="hidden.html#R2">in</a> <span class="p1">(<span class="default"><a href="relat_1.html#K2">rng</a> the <a href="graph_1.html#U3">Source</a> of <font color="Maroon">c<sub>6</sub></font></span>)</span> <a href="xboole_0.html#K2">\/</a> <span class="p1">(<span class="default"><a href="relat_1.html#K2">rng</a> the <a href="graph_1.html#U4">Target</a> of <font color="Maroon">c<sub>6</sub></font></span>)</span> &amp; 2 <a href="hidden.html#R2">in</a> <span class="p1">(<span class="default"><a href="relat_1.html#K2">rng</a> the <a href="graph_1.html#U3">Source</a> of <font color="Maroon">c<sub>6</sub></font></span>)</span> <a href="xboole_0.html#K2">\/</a> <span class="p1">(<span class="default"><a href="relat_1.html#K2">rng</a> the <a href="graph_1.html#U4">Target</a> of <font color="Maroon">c<sub>6</sub></font></span>)</span> )
 <b>by </b><i><a class="ref" href="xboole_0.html#D2">XBOOLE_0:def 2</a></i>;<br/><a NAME="E5:9_1_1_2_1_2"/><b>then </b>
( <span class="p1"><a href="tarski.html#K2">{</a><span class="default">1,2</span><a href="tarski.html#K2">}</a></span> <a href="tarski.html#R1">c=</a> the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>6</sub></font> &amp; the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>6</sub></font> <a href="tarski.html#R1">c=</a> <span class="p1"><a href="tarski.html#K2">{</a><span class="default">1,2</span><a href="tarski.html#K2">}</a></span> )
 <b>by </b><i><a class="txt" href="msscyc_1.html#E3:9_1_1_2"><i><font color="Green">E9</font></i></a>, <a class="txt" href="msscyc_1.html#E4:9_1_1_2"><i><font color="Green">E10</font></i></a>, <a class="ref" href="xboole_1.html#T7">XBOOLE_1:7</a>, <a class="ref" href="zfmisc_1.html#T38">ZFMISC_1:38</a></i>;<br/><a NAME="E6:9_1_1_2_1_2"/><b>then </b>
<span class="p1"><a href="tarski.html#K2">{</a><span class="default">1,2</span><a href="tarski.html#K2">}</a></span> <a href="hidden.html#R1">=</a> the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>6</sub></font>
 <b>by </b><i><a class="ref" href="xboole_0.html#D10">XBOOLE_0:def 10</a></i>;<br/><a NAME="E7:9_1_1_2_1_2"/><b>then </b>
( the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>7</sub></font> <a href="tarski.html#R1">c=</a> the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>7</sub></font> &amp; the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>7</sub></font> <a href="tarski.html#R1">c=</a> the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>6</sub></font> )
 <b>by </b><i><a class="txt" href="msscyc_1.html#E3:9_1_1_2"><i><font color="Green">E9</font></i></a>, <a class="ref" href="xboole_1.html#T7">XBOOLE_1:7</a></i>;<br/><b>hence </b><a NAME="E8:9_1_1_2_1_2"/>
contradiction
 <b>by </b><i><a class="txt" href="msscyc_1.html#E1:9_1_1_2"><i><font color="Green">E7</font></i></a>, <a class="ref" href="xboole_1.html#T67">XBOOLE_1:67</a></i>;<br/></div><b>end;</b></div><div><a class="txt" onclick="hsNdiv(this)" href="javascript:()" title="9_1_1_2_1_3"><b>suppose </b></a><a NAME="E1:9_1_1_2_1_3"/><i><font color="Green">E12</font></i>: 
( the <a href="graph_1.html#U2">Edges</a> of <font color="Maroon">c<sub>6</sub></font> <a href="hidden.html#R1">=</a>  <a href="xboole_0.html#K1">{}</a>  &amp; the <a href="graph_1.html#U2">Edges</a> of <font color="Maroon">c<sub>7</sub></font> <a href="hidden.html#R1">=</a> <span class="p1"><a href="tarski.html#K1">{</a><span class="default">1</span><a href="tarski.html#K1">}</a></span> )
 ;<br/><div class="add"><a NAME="E2:9_1_1_2_1_3"/><b>then </b>
( the <a href="graph_1.html#U3">Source</a> of <font color="Maroon">c<sub>7</sub></font> <a href="funct_1.html#K1">.</a> 1 <a href="hidden.html#R1">=</a> <font color="Maroon">c<sub>3</sub></font> <a href="funct_1.html#K1">.</a> 1 &amp; the <a href="graph_1.html#U4">Target</a> of <font color="Maroon">c<sub>7</sub></font> <a href="funct_1.html#K1">.</a> 1 <a href="hidden.html#R1">=</a> <font color="Maroon">c<sub>4</sub></font> <a href="funct_1.html#K1">.</a> 1 )
 <b>by </b><i><a class="txt" href="msscyc_1.html#E1:9_1_1"><i><font color="Green">E5</font></i></a>, <a class="txt" href="msscyc_1.html#E2:9_1_1_2"><i><font color="Green">E8</font></i></a>, <a class="ref" href="graph_1.html#D2">GRAPH_1:def 2</a></i>;<br/><a NAME="E3:9_1_1_2_1_3"/><b>then </b>
( 1 <a href="hidden.html#R2">in</a>  <a href="relat_1.html#K2">rng</a> the <a href="graph_1.html#U3">Source</a> of <font color="Maroon">c<sub>7</sub></font> &amp; 2 <a href="hidden.html#R2">in</a>  <a href="relat_1.html#K2">rng</a> the <a href="graph_1.html#U4">Target</a> of <font color="Maroon">c<sub>7</sub></font> )
 <b>by </b><i><a class="txt" href="msscyc_1.html#E1:9_1_1"><i><font color="Green">E5</font></i></a>, <a class="txt" href="msscyc_1.html#E5:9_1_1"><i><font color="Green">E6</font></i></a>, <a class="txt" href="msscyc_1.html#E1:9_1_1_2_1_3"><i><font color="Green">E12</font></i></a>, <a class="ref" href="funct_2.html#T6">FUNCT_2:6</a></i>;<br/><a NAME="E4:9_1_1_2_1_3"/><b>then </b>
( 1 <a href="hidden.html#R2">in</a> <span class="p1">(<span class="default"><a href="relat_1.html#K2">rng</a> the <a href="graph_1.html#U3">Source</a> of <font color="Maroon">c<sub>7</sub></font></span>)</span> <a href="xboole_0.html#K2">\/</a> <span class="p1">(<span class="default"><a href="relat_1.html#K2">rng</a> the <a href="graph_1.html#U4">Target</a> of <font color="Maroon">c<sub>7</sub></font></span>)</span> &amp; 2 <a href="hidden.html#R2">in</a> <span class="p1">(<span class="default"><a href="relat_1.html#K2">rng</a> the <a href="graph_1.html#U3">Source</a> of <font color="Maroon">c<sub>7</sub></font></span>)</span> <a href="xboole_0.html#K2">\/</a> <span class="p1">(<span class="default"><a href="relat_1.html#K2">rng</a> the <a href="graph_1.html#U4">Target</a> of <font color="Maroon">c<sub>7</sub></font></span>)</span> )
 <b>by </b><i><a class="ref" href="xboole_0.html#D2">XBOOLE_0:def 2</a></i>;<br/><a NAME="E5:9_1_1_2_1_3"/><b>then </b>
( <span class="p1"><a href="tarski.html#K2">{</a><span class="default">1,2</span><a href="tarski.html#K2">}</a></span> <a href="tarski.html#R1">c=</a> the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>7</sub></font> &amp; the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>7</sub></font> <a href="tarski.html#R1">c=</a> <span class="p1"><a href="tarski.html#K2">{</a><span class="default">1,2</span><a href="tarski.html#K2">}</a></span> )
 <b>by </b><i><a class="txt" href="msscyc_1.html#E3:9_1_1_2"><i><font color="Green">E9</font></i></a>, <a class="txt" href="msscyc_1.html#E5:9_1_1_2"><i><font color="Green">E11</font></i></a>, <a class="ref" href="xboole_1.html#T7">XBOOLE_1:7</a>, <a class="ref" href="zfmisc_1.html#T38">ZFMISC_1:38</a></i>;<br/><a NAME="E6:9_1_1_2_1_3"/><b>then </b>
<span class="p1"><a href="tarski.html#K2">{</a><span class="default">1,2</span><a href="tarski.html#K2">}</a></span> <a href="hidden.html#R1">=</a> the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>7</sub></font>
 <b>by </b><i><a class="ref" href="xboole_0.html#D10">XBOOLE_0:def 10</a></i>;<br/><a NAME="E7:9_1_1_2_1_3"/><b>then </b>
( the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>6</sub></font> <a href="tarski.html#R1">c=</a> the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>6</sub></font> &amp; the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>6</sub></font> <a href="tarski.html#R1">c=</a> the <a href="graph_1.html#U1">Vertices</a> of <font color="Maroon">c<sub>7</sub></font> )
 <b>by </b><i><a class="txt" href="msscyc_1.html#E3:9_1_1_2"><i><font color="Green">E9</font></i></a>, <a class="ref" href="xboole_1.html#T7">XBOOLE_1:7</a></i>;<br/><b>hence </b><a NAME="E8:9_1_1_2_1_3"/>
contradiction
 <b>by </b><i><a class="txt" href="msscyc_1.html#E1:9_1_1_2"><i><font color="Green">E7</font></i></a>, <a class="ref" href="xboole_1.html#T67">XBOOLE_1:67</a></i>;<br/></div><b>end;</b></div></div><b>end;</b></div>

</div><b>end;</b></div>

<b>thus </b><a NAME="E9:9_1_1"/>
not <font color="Maroon">c<sub>5</sub></font> is <a href="msscyc_1.html#V2" target="_self">empty</a>
 <b>by </b><i><a class="ref" href="msscyc_1.html#D3" target="_self">Def3</a></i>;<br/>

<b>thus </b><a NAME="E10:9_1_1"/>
<font color="Maroon">c<sub>5</sub></font> is <a href="graph_1.html#V1">strict</a>
 ;<br/>


</div>
