#triad__trio__triplet  a set of three similar things considered as a unit
  supertype:  #set.aggregation  a group of things of the same kind that belong together and are so used: "a set of books"; "a set of golf clubs"; "a set of teeth"
  subtype:  #trilogy  a set of three literary or dramatic works related in subject or theme
  subtype:  #Trimurti  the triad of divinities of later Hinduism

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