@electronic{erdosbaconsabbath.com,
   title       = {Erdős Bacon Sabbath Project}, 
   url         = {http://erdosbaconsabbath.com/},
   biburl      = {https://puma.uni-kassel.de/url/fd97799811617c3a72ea0be5afa1d07b/stephandoerfel},
   keywords    = {bacon erdős fun math sabbath},
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@electronic{www.matheboard.de,
   title       = {Eigene math. Operatoren}, 
   url         = {http://www.matheboard.de/archive/10096/thread.html},
   biburl      = {https://puma.uni-kassel.de/url/cc03021f5a0e0d1d1dc6d036f2ea28e1/stephandoerfel},
   keywords    = {DeclareMathOperator index latex math mathoperator operator tip tipp tipps tool tutorial},
   added-at    = {2011-01-26T17:07:29.000+0100},
   description = {Hilfe zu Eigene math. Operatoren .},
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}

@electronic{math.rejecta.org,
   title       = {Rejecta Mathematica | Caveat Emptor}, 
   url         = {http://math.rejecta.org/},
   biburl      = {https://puma.uni-kassel.de/url/5320ea461be99fd84bc9d9b2539a1646/stephandoerfel},
   keywords    = {info2.0 math mathematica mathematik rejecta review},
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