':param prefLabel: the preferred label for the concept
:type prefLabel: str
:param arity: the arity of the concept
:type arity: int
@keyword altLabels: other (related) labels
:type altLabels: list
@keyword closures: closure properties of the extension             (list items can be ``symmetric``, ``reflexive``, ``transitive``)
:type closures: list
@keyword extension: the extensional value of the concept
:type extension: set'

def __init__(self, prefLabel, arity, altLabels=[], closures=[], extension=set()):

    self.prefLabel = prefLabel
    self.arity = arity
    self.altLabels = altLabels
    self.closures = closures
    self._extension = extension
    self.extension = sorted(list(extension))
