If a Caccioppoli set A$A$ is of minimal perimeter in every set K compact set $K$ contained in ansome open set , can we say Athat $A$ is of minimal perimeter in the open set? If not, please construct a counterexample. This problems arises when I read lemma 9.1 in the book of Guisti ,minimal surfaces and functions of bounded variation Minimal Surfaces and Functions of Bounded Variation. The author explains "caccioppoliCaccioppoli sets of least area "in such ain this way,sometimes and sometimes he uses "caccioppoli sets of least perimeter".I am confusedthe term Caccioppoli sets of least perimeter.