@Book{hartman+2018,
  author       = {Gregory Hartman and Troy Siemers and Brian Heinold and
                  Dimplekumar Chalishajar},
  title        = {{APEX} Calculus},
  publisher    = {Self-published},
  year         = 2018,
  edition      = {Version 4.0},
  URL          = {http://www.apexcalculus.com}
}