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<b>let </b><font color="Maroon">G</font> be  non <a href="struct_0.html#V3">empty</a>  <a href="group_1.html#L1">HGrStr</a> ;<br/>

<b>thus </b><a NAME="E1:19"/>
( <font color="Maroon">G</font> is <a href="group_1.html#V2">unital</a> implies  ex <font color="Olive">a</font> being  <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">G</font> st <br/>for <font color="Olive">b</font> being  <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">G</font> holds <br/> ( <font color="Olive">a</font> <a href="group_1.html#K1">*</a> <font color="Olive">b</font> <a href="hidden.html#R1">=</a> <font color="Olive">b</font> &amp; <font color="Olive">b</font> <a href="group_1.html#K1">*</a> <font color="Olive">a</font> <a href="hidden.html#R1">=</a> <font color="Olive">b</font> ) )
 <div><a class="txt" onclick="hs2(this)" href="javascript:()" title="19_1"><b>proof </b></a><div class="add">

<b>given </b><font color="Maroon">a</font> being   <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">G</font><b> such that </b><a NAME="E1:19_1"/><i><font color="Green">E28</font></i>: 
<font color="Maroon">a</font> <a href="binop_1.html#R3">is_a_unity_wrt</a> the <a href="group_1.html#U1">mult</a> of <font color="Maroon">G</font>
 ; <i><font color="Red">:: according to </font></i><a class="ref" href="setwiseo.html#D2">SETWISEO:def 2</a>,<a class="ref" href="monoid_0.html#D10" target="_self">MONOID_0:def 10</a><br/>

<b>take </b>
<font color="Maroon">a</font>
;<br/>

<b>let </b><font color="Maroon">b</font> be   <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">G</font>;<br/>

<a NAME="E2:19_1"/>
( <font color="Maroon">a</font> <a href="group_1.html#K1">*</a> <font color="Maroon">b</font> <a href="hidden.html#R1">=</a> <font color="Maroon">H<sub>2</sub></font>(<font color="Maroon">G</font>) <a href="binop_1.html#K2">.</a> <font color="Maroon">a</font>,<font color="Maroon">b</font> &amp; <font color="Maroon">b</font> <a href="group_1.html#K1">*</a> <font color="Maroon">a</font> <a href="hidden.html#R1">=</a> <font color="Maroon">H<sub>2</sub></font>(<font color="Maroon">G</font>) <a href="binop_1.html#K2">.</a> <font color="Maroon">b</font>,<font color="Maroon">a</font> &amp; <font color="Maroon">a</font> <a href="binop_1.html#R1">is_a_left_unity_wrt</a> <font color="Maroon">H<sub>2</sub></font>(<font color="Maroon">G</font>) &amp; <font color="Maroon">a</font> <a href="binop_1.html#R2">is_a_right_unity_wrt</a> the <a href="group_1.html#U1">mult</a> of <font color="Maroon">G</font> )
 
<b>by </b><i>, <a class="ref" href="binop_1.html#D7">BINOP_1:def 7</a></i>;<br/>
<b>hence </b><a NAME="E3:19_1"/>
( <font color="Maroon">a</font> <a href="group_1.html#K1">*</a> <font color="Maroon">b</font> <a href="hidden.html#R1">=</a> <font color="Maroon">b</font> &amp; <font color="Maroon">b</font> <a href="group_1.html#K1">*</a> <font color="Maroon">a</font> <a href="hidden.html#R1">=</a> <font color="Maroon">b</font> )
 <b>by </b><i><a class="ref" href="binop_1.html#D5">BINOP_1:def 5</a>, <a class="ref" href="binop_1.html#D6">BINOP_1:def 6</a></i>;<br/>


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

<b>given </b><font color="Maroon">a</font> being   <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">G</font><b> such that </b><a NAME="E2:19"/><i><font color="Green">E39</font></i>: 
for <font color="Olive">b</font> being  <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">G</font> holds <br/> ( <font color="Maroon">a</font> <a href="group_1.html#K1">*</a> <font color="Olive">b</font> <a href="hidden.html#R1">=</a> <font color="Olive">b</font> &amp; <font color="Olive">b</font> <a href="group_1.html#K1">*</a> <font color="Maroon">a</font> <a href="hidden.html#R1">=</a> <font color="Olive">b</font> )
 ;<br/>

<b>take </b>
<font color="Maroon">a</font>
; <i><font color="Red">:: according to </font></i><a class="ref" href="setwiseo.html#D2">SETWISEO:def 2</a>,<a class="ref" href="monoid_0.html#D10" target="_self">MONOID_0:def 10</a><br/>

<b>thus </b><a NAME="E3:19"/>
<font color="Maroon">a</font> <a href="binop_1.html#R1">is_a_left_unity_wrt</a> the <a href="group_1.html#U1">mult</a> of <font color="Maroon">G</font>
  <i><font color="Red">:: according to </font></i><a class="ref" href="binop_1.html#D7">BINOP_1:def 7</a><div><a class="txt" onclick="hs2(this)" href="javascript:()" title="19_2"><b>proof </b></a><div class="add">

<b>let </b><font color="Maroon">b</font> be   <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">G</font>; <i><font color="Red">:: according to </font></i><a class="ref" href="binop_1.html#D16">BINOP_1:def 16</a><br/>

<a NAME="E1:19_2"/>
<font color="Maroon">a</font> <a href="group_1.html#K1">*</a> <font color="Maroon">b</font> <a href="hidden.html#R1">=</a> <font color="Maroon">b</font>
 
<b>by </b><i/>;<br/>
<b>hence </b><a NAME="E2:19_2"/>
the <a href="group_1.html#U1">mult</a> of <font color="Maroon">G</font> <a href="binop_1.html#K2">.</a> <font color="Maroon">a</font>,<font color="Maroon">b</font> <a href="hidden.html#R1">=</a> <font color="Maroon">b</font>
 ;<br/>


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

<b>let </b><font color="Maroon">b</font> be   <a href="struct_0.html#NM1">Element</a> of <font color="Maroon">G</font>; <i><font color="Red">:: according to </font></i><a class="ref" href="binop_1.html#D17">BINOP_1:def 17</a><br/>

<a NAME="E4:19"/>
<font color="Maroon">b</font> <a href="group_1.html#K1">*</a> <font color="Maroon">a</font> <a href="hidden.html#R1">=</a> <font color="Maroon">b</font>
 
<b>by </b><i/>;<br/>
<b>hence </b><a NAME="E5:19"/>
the <a href="group_1.html#U1">mult</a> of <font color="Maroon">G</font> <a href="binop_1.html#K2">.</a> <font color="Maroon">b</font>,<font color="Maroon">a</font> <a href="hidden.html#R1">=</a> <font color="Maroon">b</font>
 ;<br/>


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