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<a NAME="E1:6_1_1"/>
( not <font color="Maroon" title="c1">d</font> is <a href="xboole_0.html#V1" title="XBOOLE_0:attr.1">zero</a> iff <font color="Maroon" title="c1">d</font> <a href="xxreal_0.html#NR4" title="XXREAL_0:NR.4">&gt;</a> 0 )
 
;<br/>
<a NAME="E2:6_1_1"/><b>then </b>
( not <font color="Maroon" title="c1">d</font> is <a href="xboole_0.html#V1" title="XBOOLE_0:attr.1">zero</a> iff <font color="Maroon" title="c1">d</font> <a href="xxreal_0.html#NR2" title="XXREAL_0:NR.2">&gt;=</a> 1 <a href="nat_1.html#K1" title="NAT_1:func.1">+</a> 0 )
 
<b>by </b><i><a class="ref" href="nat_1.html#T13" title="NAT_1:th.13">NAT_1:13</a></i>;<br/>
<b>hence </b><a NAME="E3:6_1_1"/>
( <font color="Maroon" title="c1">d</font> is <a href="xboole_0.html#V1" title="XBOOLE_0:attr.1">zero</a> iff not <font color="Maroon" title="c1">d</font> <a href="xxreal_0.html#NR2" title="XXREAL_0:NR.2">&gt;=</a> 1 )
 ;<br/>


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