@article{MOMA_1988__106_1_178397,
     author = {B.P. Duggal},
     title = {On {Intertwining} {Operators.}},
     journal = {Monatshefte f\"ur Mathematik},
     pages = {139--148},
     publisher = {mathdoc},
     volume = {106},
     number = {1},
     year = {1988},
     zbl = {0652.47019},
     url = {http://geodesic.mathdoc.fr/item/MOMA_1988__106_1_178397/}
}