@article{MM2_1997__93_4_156305,
     author = {Martin Engman},
     title = {Trace {Formulae} for {S1} invariant {Green's} {Operators} on {S2.}},
     journal = {Manuscripta mathematica},
     pages = {357--368},
     publisher = {mathdoc},
     volume = {93},
     number = {4},
     year = {1997},
     zbl = {0882.58056},
     url = {http://geodesic.mathdoc.fr/item/MM2_1997__93_4_156305/}
}