#constant_quantity__constant  a quantity that does not vary
  supertype:  #quantity  something that has a magnitude and can be represented in mathematical expressions by a constant or a variable
  subtype:  #parametric_quantity__parameter  a constant in the equation of a curve that can be varied to yield a family of similar curves
     subtype:  #degree_of_freedom.parametric_quantity__degreeoffreedom  one of the minimum number of parameters needed to describe the state of a physical system

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