Title Outer independent {2}-domination in trees Type of Research Article Keywords Outer independent {2}-domination in trees Abstract Outer independent {2}-domination in trees Researchers M. Esmaeilian (First Researcher)، jafar amjadi (Second Researcher)، Mustapha Chellali (Third Researcher)، Seyed Mahmoud Sheikholeslami Kavkani (Fourth Researcher)