diff --git a/bib/sivanov-extra.bib b/bib/sivanov-extra.bib
index 87dd3e7..12cd489 100644
--- a/bib/sivanov-extra.bib
+++ b/bib/sivanov-extra.bib
@@ -25,3 +25,11 @@ year = {2014},
 keywords = {Reaction system; model checking; mass conservation; conserved set; conservation dependency graph; simulator},
 ISBN = {978-952-12-3123-0},
 }
+
+@article{IvanovMarcus2015,
+  Title   = {On the Lower Bounds for Leftist Insertion-Deletion Languages},
+  Author  = {Sergiu Ivanov and Sergey Verlan},
+  Journal = {Annals of the University of Bucharest (Informatics)},
+  Volume  = {LXII(2)},
+  Pages   = {77--88}
+}