diff --git a/dual-problems.bib b/dual-problems.bib
index 9b3edfc..3ea5ed1 100644
--- a/dual-problems.bib
+++ b/dual-problems.bib
@@ -17,7 +17,8 @@ @book{boffi2013mixed
   author={Boffi, Daniele and Brezzi, Franco and Fortin, Michel},
   volume={44},
   year={2013},
-  publisher={Springer}
+  publisher={Springer},
+  isbn={9783642365195}
 }
 
 
@@ -63,7 +64,8 @@ @book{nocedal2006numerical
   title={Numerical optimization},
   author={Nocedal, Jorge and Wright, Stephen},
   year={2006},
-  publisher={Springer Science \& Business Media}
+  publisher={Springer Science \& Business Media},
+  isbn={9780387400655}
 }
 
 
@@ -71,7 +73,8 @@ @book{boyd2004convex
   title={Convex optimization},
   author={Boyd, Stephen and Vandenberghe, Lieven},
   year={2004},
-  publisher={Cambridge University Press}
+  publisher={Cambridge University Press},
+  isbn={9780521833783}
 }
 
 
@@ -79,7 +82,8 @@ @book{weinstock1974calculus
   title={Calculus of variations: with applications to physics and engineering},
   author={Weinstock, Robert},
   year={1974},
-  publisher={Courier Corporation}
+  publisher={Courier Corporation},
+  isbn={9780486141060}
 }
 
 
@@ -121,7 +125,8 @@ @book{greve2009dynamics
   title={Dynamics of ice sheets and glaciers},
   author={Greve, Ralf and Blatter, Heinz},
   year={2009},
-  publisher={Springer Science \& Business Media}
+  publisher={Springer Science \& Business Media},
+  isbn={9783642034152}
 }
 
 
@@ -386,7 +391,8 @@ @book{attouch2014variational
   title={{Variational analysis in Sobolev and BV spaces: applications to PDEs and optimization}},
   author={Attouch, Hedy and Buttazzo, Giuseppe and Michaille, G{\'e}rard},
   year={2014},
-  publisher={SIAM}
+  publisher={SIAM},
+  isbn={9780898716009}
 }