Iranian Mathematical Society (IMS) Bulletin of the Iranian Mathematical Society 1017-060X 39 1 2013 03 01 $varepsilon$-Simultaneous approximations of downward sets193 203 en H. Alizadeh Islamic Aazad University, Marand, Iran Sh. Rezapour Azarbaidjan University of Tarbiat Moallem, Iran S. M. Vaezpour Amirkabir University of Technology, Iran 2011 05 20 $varepsilon$-simultaneous approximation Downward set Lattice Banach space