P: Lee studies.<BR>
Q: Lee does well.<BR>
R: Logic is interesting.<BR>
S: Logic is easy.<P>


1.  Lee will study only if logic is easy.  She will not do well unless she studies.  Logic is not easy.  Therefore, Lee will not do well.<P>  

<B>PSC, QNPO, SN |- QN</B><P>

1. PSC<BR>
2. QNPO<BR>
<U>3. SN \show QN</U><BR>
4. SNPNC...1 C subs  <I>Note that we must do this step first.</I><BR>
5. PN......3,4 C elim <I>This is a rule that requires a left-to-right movement.</I><BR>
6. QN......2,5 O elim  <I>This rules works by <U>negating</U> one of the two elements.</I><BR>

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