@MISC{NECKLA_2.MIZ,
  AUTHOR = {Retel, Krzysztof},
  TITLE = {The Class of Series-Parallel Graphs. 
{P}art {II}},
  NOTE = {This work has been partially supported by CALCULEMUS grant HPRN-CT-2000-00102.},
  DAY = {29},
  MONTH = {May},
  YEAR = {2003},
  ADDRESS1 = {University of Bia{\l}ystok},
  SUMMARY = {In this paper we introduce two new operations on graphs:
   sum and union corresponding to parallel and series
   operation respectively.
   We determine $N$-free graph as the graph that does not
   embed Necklace $4$. We define ``fin\_RelStr" as the set of
   all graphs with finite carriers.
   We also define the smallest class of graphs which contains
   the one-element graph and which is closed under parallel
   and series operations. The goal of the article is to prove
   the theorem that the class of finite series-parallel graphs
   is the class of finite $N$-free graphs. 
   This paper formalizes the next part of \cite{Thomasse}.}}

