Fix typos in Section 12.3 of the Open Logic Text

Author: FnControlOption

content/first-order-logic/axiomatic-deduction/proving-things.tex

@@ -32,7 +32,7 @@
   1. &  $\lnot !D \lif (!D \lif !E)$ & \olref[prp]{ax:lnot2} \\
   2. & $(\lnot !D \lif (!D \lif !E)) \lif {}$\\
   &\qquad $((!E \lif (!D \lif !E)) \lif ((\lnot !D \lor !E) \lif (!D \lif !E)))$ & \olref[prp]{ax:lor3}\\
-  3. & $((!E \lif (!D \lif !E)) \lif ((\lnot !D \lor !E) \lif (!D \lif !E))$ & 1, 2, \MP\\
+  3. & $(!E \lif (!D \lif !E)) \lif ((\lnot !D \lor !E) \lif (!D \lif !E))$ & 1, 2, \MP\\
   4. & $!E \lif (!D \lif !E)$ & \olref[prp]{ax:lif1}\\
   5. & $(\lnot !D \lor !E) \lif (!D \lif !E)$ & 3, 4, \MP
 \end{derivation}
@@ -111,10 +111,10 @@
   lines 3--7 of the !!{derivation} in the preceding example. This is
   !!a{derivation} of $!A \lif !C$---which is the last line of the new
   !!{derivation}---from~$\Gamma$. Note that the justifications of
-  lines 4 and~7 remain valid if the reference to line number~2 is
+  lines 4 and~7 remain valid if the reference to line number~1 is
   replaced by reference to the last line of the !!{derivation} of~$!A
-  \lif !B$, and reference to line number~1 by reference to the last
-  line of the !!{derivation} of~$B \lif !C$.
+  \lif !B$, and reference to line number~2 by reference to the last
+  line of the !!{derivation} of~$!B \lif !C$.
 \end{proof}
 
 \begin{prob}