@article { author = {Samodivkin, Vladimir}, title = {Hypo-efficient domination and hypo-unique domination}, journal = {Communications in Combinatorics and Optimization}, volume = {1}, number = {2}, pages = {103-116}, year = {2016}, publisher = {Azarbaijan Shahid Madani University}, issn = {2538-2128}, eissn = {2538-2136}, doi = {10.22049/cco.2016.13553}, abstract = {For a graph $G$ let $\gamma (G)$ be its domination number. We define a graph G to be (i)  a  hypo-efficient domination graph (or  a  hypo-$\mathcal{ED}$ graph) if $G$ has no  efficient dominating set (EDS)  but every graph formed by removing a single vertex from $G$ has at least one EDS, and (ii)  a hypo-unique domination graph (a hypo-$\mathcal{UD}$ graph) if $G$ has at least two  minimum dominating sets, but $G-v$ has a unique minimum dominating set  for each $v\in V(G)$. We  show that each  hypo-$\mathcal{UD}$ graph $G$ of order at least $3$  is connected  and $\gamma(G-v) <\gamma(G)$ for all $v \in V$. We obtain a tight  upper bound  on the order of a hypo-$\mathcal{P}$ graph in terms of the domination number and maximum degree of the graph, where $\mathcal{P} \in \{\mathcal{UD}, \mathcal{ED}\}$.  Families of  circulant graphs, which achieve these bounds, are presented. We also prove that the bondage number of any  hypo-$\mathcal{UD}$ graph is not more than the minimum degree plus one.  }, keywords = {Domination number,Efficient Domination,unique domination,hypo-property}, url = {http://comb-opt.azaruniv.ac.ir/article_13553.html}, eprint = {http://comb-opt.azaruniv.ac.ir/article_13553_2afb7e049e6640f7612ba8d81256137c.pdf} }