#irrational_number  a real number that cannot be expressed as a rational number
  supertype:  #real_number__real  any rational or irrational number
  subtype:  #transcendental_number  an irrational number that is not algebraic
  subtype:  #algebraic_number__algebraicnumber  root of an algebraic equation with rational coefficients
  subtype:  #3.14159265358979323846...__pi  the ratio of the circumference to the diameter of a circle
  subtype:  #e__2.718282...  the base of the natural system of logarithms

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