#real_matrix  a matrix whose elements are all real numbers
  supertype:  #matrix  a rectangular array of elements (or entries) set out by rows and columns
     supertype:  #array  an orderly arrangement: "an array of troops in battle order"
        supertype:  #arrangement  an orderly grouping (of things or persons)
           supertype:  #group__grouping  any number of entities (members) considered as a unit
              supertype:  pm#collection  something gathering separated things (entities/situations)
                 supertype:  pm#divisible_entity__divisibleentity  many classifications under this category are application-dependant
                    supertype:  pm#entity  something that can be "involved" in a situation
                       supertype:  pm#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:  pm#divisible_thing__divisiblething
                       supertype:  pm#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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