Added relevant Hahn-Banach results.

refs.bib

@@ -74,3 +74,13 @@
   year={2014},
   publisher={European Mathematical Society}
 }
+@book{Brezis,
+  title={Functional Analysis, Sobolev Spaces and Partial Differential Equations},
+  author={Brezis, H.},
+  isbn={9780387709130},
+  lccn={2010938382},
+  series={Universitext},
+  url={https://books.google.ca/books?id=GAA2XqOIIGoC},
+  year={2010},
+  publisher={Springer New York}
+}