#variable.symbol  a symbol (like x or y) that is used in mathematical or logical expressions to represent a variable quantity
  supertype:  #symbol  an arbitrary sign (written or printed) that has acquired a conventional significance
  subtype:  #placeholder  a symbol in a logical or mathematical expression that can be replaced by the name of any member of specified set
  subtype:  #unknown__unknown_quantity__unknownquantity  a variable whose values are solutions of an equation

No statement uses or specializes #variable.symbol; click here to add one.