R123 - modelint/shlaer-mellor-metamodel GitHub Wiki
R123 / 1:1
Symmetric Perspective is view on exactly one Unary Association
Unary Association is viewed from exactly one Symmetric Perspective
A Unary Association is formed with, by definition, only one Perspective referred to as the S
Perspective.
Formalization
Symmetric Perspective.(Rnum, Domain) -> Unary Association.(Rnum, Domain)