@MISC{ABSVALUE.MIZ,
  AUTHOR = {Popio{\l}ek, Jan},
  TITLE = {Some Properties of Functions
Modul and Signum},
  DAY = {21},
  MONTH = {June},
  YEAR = {1989},
  ADDRESS1 = {Warsaw University\\Bia{\l}ystok},
  SUMMARY = {The article includes definitions and theorems concerning basic
properties of the following functions: $|x|$ -- modul of real number,
sgn $x$ -- signum of real number.}}

