#pure_imaginary_number  an imaginary number of the form a+bi where a is 0
  supertype:  complex_number__complexnumber__complex_quantity__complexquantity__imaginary_number__imaginarynumber  a number of the form a+bi where a and b are real numbers and i is the square root of -1
  subtype:  imaginary_part_of_a_complex_number__imaginary_part__imaginarypart  the part of a complex number that has the square root of -1 as a factor

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