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<b>let </b><font color="Maroon">H</font> be   <a href="zf_lang.html#NM2">ZF-formula</a>;<br/><b>let </b><font color="Maroon">x</font> be   <a href="zf_lang.html#NM1">Variable</a>;<br/><b>let </b><font color="Maroon">y</font> be   <a href="zf_lang.html#NM1">Variable</a>;<br/><b>let </b><font color="Maroon">M</font> be  non <a href="xboole_0.html#V1">empty</a>  <a href="hidden.html#M1">set</a> ;<br/>







<a NAME="E1:91"/>
( ( <font color="Maroon">M</font> <a href="zf_model.html#R2">|=</a> <font color="Maroon">H</font> implies <font color="Maroon">M</font> <a href="zf_model.html#R2">|=</a>  <a href="zf_lang.html#K13">Ex</a> <font color="Maroon">y</font>,<font color="Maroon">H</font> ) &amp; ( <font color="Maroon">M</font> <a href="zf_model.html#R2">|=</a>  <a href="zf_lang.html#K13">Ex</a> <font color="Maroon">y</font>,<font color="Maroon">H</font> implies <font color="Maroon">M</font> <a href="zf_model.html#R2">|=</a>  <a href="zf_lang.html#K15">Ex</a> <font color="Maroon">x</font>,<font color="Maroon">y</font>,<font color="Maroon">H</font> ) )
 
<b>by </b><i/>;<br/>
<b>hence </b><a NAME="E2:91"/>
( <font color="Maroon">M</font> <a href="zf_model.html#R2">|=</a> <font color="Maroon">H</font> implies <font color="Maroon">M</font> <a href="zf_model.html#R2">|=</a>  <a href="zf_lang.html#K15">Ex</a> <font color="Maroon">x</font>,<font color="Maroon">y</font>,<font color="Maroon">H</font> )
 ;<br/>


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