On the number of additional edges of a~minimal vertex 1-extension of a~starlike tree

M. B. Abrosimov

Izvestiya of Saratov University. Mathematics. Mechanics. Informatics, Tome 12 (2012) no. 2, pp. 103-113

Résumé

For a given graph $G$ with $n$ nodes, we say that graph $G^*$ is its 1-vertex extension if for each vertex $v$ of $G^*$ the subgraph $G^*-v$ contains graph $G$ up to isomorphism. A graph $G^*$ is a minimal vertex 1-extension of the graph $G$ if $G^*$ has $n+1$ nodes and there is no 1-vertex extension with $n+1$ nodes of $G$ having fewer edges than $G^*$. A tree is called starlike if it has exactly one node of degree greater than two. We give a lower and upper bounds of the edge number of a minimal vertex 1-extension of a starlike tree and present trees on which these bounds are achieved.