An parameter slot is a unary function from COMPONENTs to parameter values. There is no intermediate parameter object when using parameter slots, since the function itself serves as the name of the parameter.
(=> (Used-In-Constraint $X $Y) (Parameter-Slot $X))
(=> (Has-Parameter-Slot $X $Y) (Parameter-Slot $Y))
(<= (Domain $X Component) (Parameter-Slot $X))
(=> (Parameter-Slot ?Unary-Function)
(Domain ?Unary-Function Component))