Fixed typo in important-sets.tex

content/sets-functions-relations/sets/important-sets.tex

@@ -33,7 +33,7 @@
 Equally, it should be clear that $\Nat \subsetneq \Int \subsetneq
 \Rat$, since $-1$ is an integer but not a natural number, and
 $\nicefrac{1}{2}$ is rational but not integer. It is less obvious
-that $\Real \subsetneq \Rat$, i.e., that there are some real numbers
+that $\Rat \subsetneq \Real$, i.e., that there are some real numbers
 which are not rational\oliflabeldef{sfr:arith:real:realline}{, but we'll
 return to this in \olref[arith][real]{realline}}{}.