#variable_quantity__variable  a quantity that can assume any of a set of values
  supertype:  quantity  something that has a magnitude and can be represented in mathematical expressions by a constant or a variable
  subtype:  independent_variable__independentvariable  a variable in a logical or mathematical expression whose value determines the dependent variable; if f(x)=y, x is the independent variable
  subtype:  correlate  either of two correlated variables
  subtype:  degree_of_freedom  an unrestricted variable in a frequency distribution
  subtype:  dependent_variable__dependentvariable  a variable in a logical or mathematical expression whose value depends in the independent variable; if f(x)=y, y is the dependent variable
  subtype:  random_variable__variate__variant__stochasticvariable__chance_variable  a variable quantity that is random
  subtype:  scalar  a variable quantity that cannot be resolved into components
  subtype:  tensor.variable_quantity  a generalization of the concept of a vector
  subtype:  vector  a variable quantity that can be resolved into components
     subtype:  vector_product__cross_product__crossproduct  a vector that is the product of two other vectors
     subtype:  vector_sum__resultant  a vector that is the sum of two or more other vectors
     subtype:  radius_vector  a line connecting a point in space to the origin of a polar coordinate system
     subtype:  radius_vector.vector__radiusvector  a line connecting a satellite to the center of the body around which it is rotating

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