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<b>let </b><font color="Maroon">c<sub>1</sub></font> be   <a href="osalg_1.html#NM3">OrderSortedSign</a>;<br/><b>let </b><font color="Maroon">c<sub>2</sub></font>, <font color="Maroon">c<sub>3</sub></font> be  <a href="msualg_1.html#V5">non-empty</a> <a href="osalg_1.html#NM5">OSAlgebra</a> of <font color="Maroon">c<sub>1</sub></font>;<br/>



<b>assume </b><a NAME="E1:12"/>
<font color="Maroon">c<sub>2</sub></font>,<font color="Maroon">c<sub>3</sub></font> <a href="osalg_3.html#R1" target="_self">are_os_isomorphic</a> 
 ;<br/>

<b>then consider </b><font color="Maroon">c<sub>4</sub></font> being   <a href="msualg_3.html#NM1">ManySortedFunction</a> of <font color="Maroon">c<sub>2</sub></font>,<font color="Maroon">c<sub>3</sub></font><b> such that </b><br/><a NAME="E3:12"/><i><font color="Green">E11</font></i>: 
( <font color="Maroon">c<sub>4</sub></font> <a href="msualg_3.html#R4">is_isomorphism</a> <font color="Maroon">c<sub>2</sub></font>,<font color="Maroon">c<sub>3</sub></font> &amp; <font color="Maroon">c<sub>4</sub></font> is <a href="osalg_3.html#V1" target="_self">order-sorted</a> )
 <b>by </b><i><a class="ref" href="osalg_3.html#D2" target="_self">Def2</a></i>;<br/>
<b>reconsider </b><font color="Maroon">c<sub>5</sub></font> = <font color="Maroon">c<sub>4</sub></font> <a href="msualg_3.html#K4">""</a>  as   <a href="msualg_3.html#NM1">ManySortedFunction</a> of <font color="Maroon">c<sub>3</sub></font>,<font color="Maroon">c<sub>2</sub></font> ;<br/>
<a NAME="E5:12"/><i><font color="Green">E12</font></i>: 
<font color="Maroon">c<sub>5</sub></font> <a href="msualg_3.html#R4">is_isomorphism</a> <font color="Maroon">c<sub>3</sub></font>,<font color="Maroon">c<sub>2</sub></font>
 
<b>by </b><i><a class="txt" href="osalg_3.html#E3:12"><i><font color="Green">E11</font></i></a>, <a class="ref" href="msualg_3.html#T14">MSUALG_3:14</a></i>;<br/>
<a NAME="E6:12"/><i><font color="Green">E13</font></i>: 
( the <a href="msualg_1.html#U4">Sorts</a> of <font color="Maroon">c<sub>2</sub></font> is   <a href="osalg_1.html#NM4">OrderSortedSet</a> of <font color="Maroon">c<sub>1</sub></font> &amp; the <a href="msualg_1.html#U4">Sorts</a> of <font color="Maroon">c<sub>3</sub></font> is   <a href="osalg_1.html#NM4">OrderSortedSet</a> of <font color="Maroon">c<sub>1</sub></font> )
 
<b>by </b><i><a class="ref" href="osalg_1.html#T17">OSALG_1:17</a></i>;<br/>
<a NAME="E7:12"/>
( <font color="Maroon">c<sub>4</sub></font> is <a href="msualg_3.html#V2">"onto"</a> &amp; <font color="Maroon">c<sub>4</sub></font> is <a href="msualg_3.html#V1">"1-1"</a> )
 
<b>by </b><i><a class="txt" href="osalg_3.html#E3:12"><i><font color="Green">E11</font></i></a>, <a class="ref" href="msualg_3.html#T13">MSUALG_3:13</a></i>;<br/>
<a NAME="E8:12"/><b>then </b>
<font color="Maroon">c<sub>4</sub></font> <a href="msualg_3.html#K4">""</a>  is <a href="osalg_3.html#V1" target="_self">order-sorted</a>
 
<b>by </b><i><a class="txt" href="osalg_3.html#E3:12"><i><font color="Green">E11</font></i></a>, <a class="txt" href="osalg_3.html#E6:12"><i><font color="Green">E13</font></i></a>, <a class="ref" href="osalg_3.html#T7" target="_self">Th7</a></i>;<br/>
<b>hence </b><a NAME="E9:12"/>
<font color="Maroon">c<sub>3</sub></font>,<font color="Maroon">c<sub>2</sub></font> <a href="osalg_3.html#R1" target="_self">are_os_isomorphic</a> 
 <b>by </b><i><a class="txt" href="osalg_3.html#E5:12"><i><font color="Green">E12</font></i></a>, <a class="ref" href="osalg_3.html#D2" target="_self">Def2</a></i>;<br/>


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