(parents tag) (parents h tag)
Returns the immediate parents of tag, either via a Java type inheritance relationship or a relationship established via derive. h must be a hierarchy obtained from make-hierarchy, if not supplied defaults to the global hierarchy
;; simple example showing single parented derivation
;; then adding another parent
user=> (derive ::toy_poodle ::poodle)
nil
user=> (parents ::toy_poodle)
#{:user/poodle}
user=> (derive ::toy_poodle ::toy_dogs)
nil
user=> (parents ::toy_poodle)
#{:user/poodle :user/toy_dogs}
user=>