#provitamin  vitamin precursor; a substance that is converted into a vitamin in animal tissues
  supertype:  #hydrocarbon  an organic compound containing only carbon and hydrogen
  subtype:  #provitamin_A__carotene__carotin  an orange isomer of an unsaturated hydrocarbon found in many plants; is converted into vitamin A in the liver
     subtype:  #beta-carotene  an isomer of carotene that is found in dark green and dark yellow fruits and vegetables

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