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<b>let </b><font color="Maroon">G1</font> be   <a href="graph_1.html#NM1">Graph</a>;<br/><b>let </b><font color="Maroon">G2</font> be   <a href="graph_1.html#NM1">Graph</a>;<br/>



<b>assume </b><a NAME="E1:55"/>
( the <a href="graph_1.html#U3" target="_self">Source</a> of <font color="Maroon">G1</font> <a href="partfun1.html#R1">tolerates</a> the <a href="graph_1.html#U3" target="_self">Source</a> of <font color="Maroon">G2</font> &amp; the <a href="graph_1.html#U4" target="_self">Target</a> of <font color="Maroon">G1</font> <a href="partfun1.html#R1">tolerates</a> the <a href="graph_1.html#U4" target="_self">Target</a> of <font color="Maroon">G2</font> )
 ;<br/>

<a NAME="E2:55"/><b>then </b>
<font color="Maroon">G1</font> <a href="graph_1.html#K1" target="_self">\/</a> <font color="Maroon">G2</font> <a href="graph_1.html#R1" target="_self">is_sum_of</a> <font color="Maroon">G1</font>,<font color="Maroon">G2</font>
 
<b>by </b><i/>;<br/>
<b>hence </b><a NAME="E3:55"/>
( <font color="Maroon">G1</font> <a href="graph_1.html#R4" target="_self">c=</a> <font color="Maroon">G1</font> <a href="graph_1.html#K1" target="_self">\/</a> <font color="Maroon">G2</font> &amp; <font color="Maroon">G2</font> <a href="graph_1.html#R4" target="_self">c=</a> <font color="Maroon">G1</font> <a href="graph_1.html#K1" target="_self">\/</a> <font color="Maroon">G2</font> )
 <b>by </b><i/>;<br/>


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