Non-abelian extensions have nonsimple spectrum
Compositio Mathematica, Tome 65 (1988) no. 2, pp. 155-170. 
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     author = {Robinson, E. Arthur},
     title = {Non-abelian extensions have nonsimple spectrum},
     journal = {Compositio Mathematica},
     pages = {155--170},
     publisher = {Kluwer Academic Publishers},
     volume = {65},
     number = {2},
     year = {1988},
     mrnumber = {932641},
     zbl = {0641.28011},
     language = {en},
     url = {http://archive.numdam.org/item/CM_1988__65_2_155_0/}
}
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Robinson, E. Arthur. Non-abelian extensions have nonsimple spectrum. Compositio Mathematica, Tome 65 (1988) no. 2, pp. 155-170. http://archive.numdam.org/item/CM_1988__65_2_155_0/

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