  The combined effects of hole doping and magnetic dilution on a lamellar
Heisenberg antiferromagnet are studied in the framework of the frustration
model. Magnetic vacancies are argued to remove some of the frustrating bonds
generated by the holes, thus explaining the increase in the temperature and
concentration ranges exhibiting three dimensional long range order. The
dependence of the Neel temperature on both hole and vacancy concentrations is
derived quantitatively from earlier renormalization group calculations for the
non--dilute case, and the results reproduce experimental data with no new
adjustable parameters.
