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<b>let </b><font color="Maroon">a</font> be   <a href="int_1.html#NM1">Integer</a>;<br/><b>let </b><font color="Maroon">b</font> be   <a href="int_1.html#NM1">Integer</a>;<br/>



<a NAME="E1:21"/>
<span class="p1">(<span class="default"><a href="int_2.html#K1" target="_self">abs</a> <font color="Maroon">a</font></span>)</span> <a href="nat_1.html#K10">hcf</a> <span class="p1">(<span class="default"><a href="int_2.html#K1" target="_self">abs</a> <font color="Maroon">b</font></span>)</span> <a href="nat_1.html#R1">divides</a>  <a href="int_2.html#K1" target="_self">abs</a> <font color="Maroon">a</font>
 
<b>by </b><i><a class="ref" href="nat_1.html#D5">NAT_1:def 5</a></i>;<br/>
<b>then consider </b><font color="Maroon">m</font> being   <a href="nat_1.html#NM1">Nat</a><b> such that </b><br/><a NAME="E3:21"/><i><font color="Green">E10</font></i>: 
 <a href="int_2.html#K1" target="_self">abs</a> <font color="Maroon">a</font> <a href="hidden.html#R1">=</a> <span class="p1">(<span class="default"><span class="p2">(<span class="default"><a href="int_2.html#K1" target="_self">abs</a> <font color="Maroon">a</font></span>)</span> <a href="nat_1.html#K10">hcf</a> <span class="p2">(<span class="default"><a href="int_2.html#K1" target="_self">abs</a> <font color="Maroon">b</font></span>)</span></span>)</span> <a href="xcmplx_0.html#K3">*</a> <font color="Maroon">m</font>
 <b>by </b><i><a class="ref" href="nat_1.html#D3">NAT_1:def 3</a></i>;<br/>
<a NAME="E4:21"/><i><font color="Green">E11</font></i>: 
( <font color="Maroon">a</font> <a href="xxreal_0.html#NR2" target="_self">&gt;=</a> 0 implies <font color="Maroon">a</font> <a href="int_2.html#K3" target="_self">gcd</a> <font color="Maroon">b</font> <a href="int_1.html#R2">divides</a> <font color="Maroon">a</font> )
 
<div><a class="txt" onclick="hs2(this)" href="javascript:()" title="21_1"><b>proof </b></a><div class="add">

<b>assume </b><a NAME="E1:21_1"/><i><font color="Green">E12</font></i>: 
<font color="Maroon">a</font> <a href="xxreal_0.html#NR2" target="_self">&gt;=</a> 0
 ;<br/>

<b>reconsider </b><font color="Maroon">c</font> = <span class="p1">(<span class="default"><a href="int_2.html#K1" target="_self">abs</a> <font color="Maroon">a</font></span>)</span> <a href="nat_1.html#K10">hcf</a> <span class="p1">(<span class="default"><a href="int_2.html#K1" target="_self">abs</a> <font color="Maroon">b</font></span>)</span> as   <a href="int_1.html#NM1">Integer</a> ;<br/>
<b>reconsider </b><font color="Maroon">a1</font> = <font color="Maroon">m</font> as   <a href="int_1.html#NM1">Integer</a> ;<br/>
<a NAME="E4:21_1"/>
<font color="Maroon">a</font> <a href="hidden.html#R1">=</a> <font color="Maroon">c</font> <a href="xcmplx_0.html#K3">*</a> <font color="Maroon">a1</font>
 
<b>by </b><i><a class="ref" href="int_2.html#T4" target="_self">Th4</a>, , <a class="ref" href="absvalue.html#D1">ABSVALUE:def 1</a></i>;<br/>
<b>hence </b><a NAME="E5:21_1"/>
<font color="Maroon">a</font> <a href="int_2.html#K3" target="_self">gcd</a> <font color="Maroon">b</font> <a href="int_1.html#R2">divides</a> <font color="Maroon">a</font>
 <b>by </b><i><a class="ref" href="int_1.html#D9">INT_1:def 9</a></i>;<br/>


</div><b>end;</b></div>
<a NAME="E5:21"/>
( <font color="Maroon">a</font> <a href="xxreal_0.html#NR3" target="_self">&lt;</a> 0 implies <font color="Maroon">a</font> <a href="int_2.html#K3" target="_self">gcd</a> <font color="Maroon">b</font> <a href="int_1.html#R2">divides</a> <font color="Maroon">a</font> )
 
<div><a class="txt" onclick="hs2(this)" href="javascript:()" title="21_2"><b>proof </b></a><div class="add">

<b>assume </b><a NAME="E1:21_2"/><i><font color="Green">E16</font></i>: 
<font color="Maroon">a</font> <a href="xxreal_0.html#NR3" target="_self">&lt;</a> 0
 ;<br/>

<b>reconsider </b><font color="Maroon">c</font> = <span class="p1">(<span class="default"><a href="int_2.html#K1" target="_self">abs</a> <font color="Maroon">a</font></span>)</span> <a href="nat_1.html#K10">hcf</a> <span class="p1">(<span class="default"><a href="int_2.html#K1" target="_self">abs</a> <font color="Maroon">b</font></span>)</span> as   <a href="int_1.html#NM1">Integer</a> ;<br/>
<b>reconsider </b><font color="Maroon">b1</font> = <font color="Maroon">m</font> as   <a href="int_1.html#NM1">Integer</a> ;<br/>
 <a href="xcmplx_0.html#K4">-</a> <span class="p1">(<span class="default"><a href="xcmplx_0.html#K4">-</a> <font color="Maroon">a</font></span>)</span> = 
 <a href="xcmplx_0.html#K4">-</a> <span class="p1">(<span class="default"><font color="Maroon">c</font> <a href="xcmplx_0.html#K3">*</a> <font color="Maroon">b1</font></span>)</span>
<b>by </b><i><a class="ref" href="int_2.html#T4" target="_self">Th4</a>, , <a class="ref" href="absvalue.html#D1">ABSVALUE:def 1</a></i>
<br/>.= 
<font color="Maroon">c</font> <a href="xcmplx_0.html#K3">*</a> <span class="p1">(<span class="default"><a href="xcmplx_0.html#K4">-</a> <font color="Maroon">b1</font></span>)</span>

;<br/>
<b>hence </b><a NAME="E5:21_2"/>
<font color="Maroon">a</font> <a href="int_2.html#K3" target="_self">gcd</a> <font color="Maroon">b</font> <a href="int_1.html#R2">divides</a> <font color="Maroon">a</font>
 <b>by </b><i><a class="ref" href="int_1.html#D9">INT_1:def 9</a></i>;<br/>


</div><b>end;</b></div>
<b>hence </b><a NAME="E6:21"/>
<font color="Maroon">a</font> <a href="int_2.html#K3" target="_self">gcd</a> <font color="Maroon">b</font> <a href="int_1.html#R2">divides</a> <font color="Maroon">a</font>
 <b>by </b><i/>;<br/>


</div>
