#metric_space  a set of points such that for every pair of points there is a nonnegative real number called their distance that is symmetric and satisfies the triangle inequality
  subtype:  Euclidean_space  Hilbert_space
  supertype:  topological_space__topologicalspace__space  (mathematics) any set of points that satisfy a set of postulates of some kind; "assume the vector space is finite dimensional"
     supertype:  set  (mathematics) an abstract collection of numbers or symbols; "the set of prime numbers is infinite"
        supertype:  collection  something gathering separated things (entities/situations)
           supertype:  divisible_entity__divisibleentity  many classifications under this category are application-dependant
              supertype:  entity  something that can be "involved" in a situation
                 supertype:  thing__something___T__t___3D_or_4D_thing_or_anything_else  any category (type or individual) is instance of this type; any type is also a subtype of this type
              supertype:  divisible_thing__divisiblething
                 supertype:  thing__something___T__t___3D_or_4D_thing_or_anything_else  any category (type or individual) is instance of this type; any type is also a subtype of this type

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