@Manual{R-base,
  title = {R: A Language and Environment for Statistical
    Computing},
  author = {{R Core Team}},
  organization = {R Foundation for Statistical Computing},
  address = {Vienna, Austria},
  year = {2017},
  url = {https://www.R-project.org/},
}


@manual{sagemath,
  Key          = {SageMath},
  Author       = {{The Sage Developers}},
  Title        = {{S}ageMath, the {S}age {M}athematics {S}oftware {S}ystem ({V}ersion 8.3)},
  note         = {{\tt https://www.sagemath.org}},
  Year         = {2018},
}


@manual{cocalc,
  Key          = {CoCalc},
  Author       = {The CoCalc Authors},
  Title        = {{Collaborative Calculation in the Cloud}},
  note         = {{\tt https://www.cocalc.com}},
  Year         = {2018},
}