doc-src/TutorialI/Overview/LNCS/document/root.bib

replaced apply-style proof for instance Multiset :: plus_ac0 by recommended Isar proof style

@string{LNCS="Lect.\ Notes in Comp.\ Sci."}
@string{Springer="Springer-Verlag"}

@book{LNCS2283,author={Tobias Nipkow and Lawrence Paulson and Markus Wenzel},
title="Isabelle/HOL --- A Proof Assistant for Higher-Order Logic",
publisher=Springer,series=LNCS,volume=2283,year=2002,
note={\url{http://www.in.tum.de/~nipkow/LNCS2283/}}}