A set SâV(G) is a semitotal dominating set of a graph G ifâ
âit is a dominating set of G andâ
âevery vertex in S is within distance 2 of another vertex of Sâ. âTheâ
âsemitotal domination number Îłt2â(G) is the minimumâ
âcardinality of a semitotal dominating set of Gâ.
âWe show that the semitotal domination problem isâ
âAPX-complete for bounded-degree graphsâ, âand the semitotal domination problem in any graph of maximum degree Î can be approximated with an approximationâ
âratio of 2+ln(Îâ1)