Let $G=(L,R;E)$ be a bipartite graph with color classes $L$ and $R$ and edge set $E$. A set of two bijections $\{\varphi_1 , \varphi_2\}$, $\varphi_1 , \varphi_2 :L \cup R \to L \cup R$, is said to be a $3$-biplacement of $G$ if $\varphi_1(L)= \varphi_2(L) = L$ and $E \cap \varphi_1^*(E)=\emptyset$, $E \cap \varphi_2^*(E)=\emptyset$, $\varphi_1^*(E) \cap \varphi_2^*(E)=\emptyset$, where$\varphi_1^*$, $\varphi_2^*$ are the maps defined on $E$, induced by $\varphi_1$, $\varphi_2$, respectively. We prove that if $|L|=p$, $|R|=q$, $3 \leq p \leq q$, then every graph $G=(L,R;E)$ of size at most $p$ has a $3$-biplacement.
(Data obrony: 2008) Adamus, Lech Wydział Matematyki Stosowanej
The aim of this thesis is to present sufficient conditions for existence of long cycles in simple graphs and in directed graphs, that is, cycles which pass through more than half of the vertices in a given graph. Namely, we want to find the minimal size of a given graph G guaranteeing that a cycle of prescribed length is contained in G. Optionally we consider a modification of this condition by adding a bound on the minimal degree of G. We investigate this problem for simple graphs, particularly bipartite, and also for digraphs, where all possible orientations of a cycle of given length are considered.
