In the paper it is proved that each generalized boundary value problem for the n-th order linear differential equation generates a Fredholm mapping of index zero.
@article{107524, author = {Boris Rudolf}, title = {The generalized boundary value problem is a Fredholm mapping of index zero}, journal = {Archivum Mathematicum}, volume = {031}, year = {1995}, pages = {55-58}, zbl = {0830.34013}, mrnumber = {1342375}, language = {en}, url = {http://dml.mathdoc.fr/item/107524} }
Rudolf, Boris. The generalized boundary value problem is a Fredholm mapping of index zero. Archivum Mathematicum, Tome 031 (1995) pp. 55-58. http://gdmltest.u-ga.fr/item/107524/
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