#fraction  the quotient of two rational numbers
  supertype:  #rational_number  an integer or a fraction
  subtype:  #mantissa__fixed-point_part__fixedpointpart  the positive fractional part of the representation of a logarithm; in the expression log 643 = 2.808 the mantissa is .808
  subtype:  #common_fraction__simple_fraction  the quotient of two integers
     subtype:  #half__one-half__onehalf  one of two equal parts of a divisible whole; "half a loaf" or "half an hour" or "a century and one half"
        subtype:  #fifty_percent__fiftypercent  a half expressed as a percentage
        subtype:  #mediety__moiety  one of two (approximately) equal parts
     subtype:  #one-third__onethird__third__tierce  one of three equal parts of a divisible whole; "it contains approximately a third of the minimum daily requirement"
     subtype:  #two-thirds  two of three equal parts of a divisible whole
     subtype:  #one-fourth__onefourth__fourth__quarter__fourth_part__twenty-five_percent__quartern  one of four equal parts; "a quarter of a pound"
     subtype:  #three-fourths__threefourth  three of four equal parts; "three-fourths of a pound"
     subtype:  #one-fifth__onefifth__fifth__fifth_part__fifthpart__twenty_percent  a fifth part
     subtype:  #one-sixth__onesixth__sixth  a sixth part
     subtype:  #one-seventh__oneseventh__seventh  a seventh part
     subtype:  #one-eighth__oneeighth__eighth  an eighth part
     subtype:  #one-ninth__oneninth__ninth  a ninth part
     subtype:  #one-tenth__onetenth__tenth__tenthpart__ten_percent__tenpercent  a tenth part; one part in ten
     subtype:  #one-hundredth__onehundredth__hundredth__onepercent  one part in a hundred
     subtype:  #one-thousandth__onethousandth__thousandth  one part in a thousand
     subtype:  #one-millionth__onemillionth__millionth  one part in a million
     subtype:  #one-billionth__onebillionth__billionth  one part in a billion
     subtype:  #one-trillionth__onetrillionth__trillionth  one part in a trillion
     subtype:  #one-quadrillionth__onequadrillionth__quadrillionth  one part in a quadrillion
     subtype:  #one-quintillionth__quintillionth  one part in a quintillion
  subtype:  #improper_fraction  a fraction whose numerator is larger than the denominator
  subtype:  #proper_fraction__properfraction  a fraction with a numerator smaller than the denominator
     subtype:  #decimal_fraction__decimalfraction__decimal  a proper fraction whose denominator is a power of 10
        subtype:  #circulating_decimal__circulatingdecimal__recurring_decimal__recurringdecimal__repeating_decimal__repeatingdecimal  a decimal with a sequence of digits that repeats itself indefinitely
  subtype:  #complex_fraction__complexfraction__compoundfraction  a fraction with fractions in the numerator or denominator
  subtype:  #continued_fraction__continuedfraction  a fraction whose numerator is an integer and whose denominator is an integer plus a fraction whose numerator is an integer and whose denominator is an integer plus a fraction and so on

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