2.3

literature.bib

@@ -42,4 +42,10 @@
   year = {2013},
   note = {Chapter 2}
 }
-
+@misc{source_patent,
+  author = {Lawrence J. Fogel},
+  title = {Apparatus for improving intelligence under high ambient noise levels},
+  howpublished = {United States Patent Office},
+  year = {1960},
+  note = {Pat. Nr. 2966549}
+}