@article{NUMA_1976__27_132436,
     author = {T. K\"upper},
     title = {Pointwise {Lower} and {Upper} {Bounds} for {Eigenfunctions} of {Ordinary} {Differential} {Operators.}},
     journal = {Numerische Mathematik},
     pages = {111--120},
     publisher = {mathdoc},
     volume = {27},
     year = {1976},
     zbl = {0324.65040},
     url = {http://geodesic.mathdoc.fr/item/NUMA_1976__27_132436/}
}