Relative clauses (RCs) in Persian are head-modifying constituents, all typically introduced by the invariant complementizer ke. Persian RCs are Unbounded Dependency Constructions (UDCs), containing either a gap or a resumptive pronoun (RP). In some positions only gaps are allowed, and in other positions only RPs. There are also some positions where both gaps and RPs are alternatively allowed. Illustrating the striking similarities between Persian gaps and RPs, I will provide an HPSG unified approach to take care of the dependency between the licensing structure and the gap/RP with a single mechanism, using only the SLASH feature. Similar to Pollard and Sag s (1994) approach to the bottom of the dependency, I will assume a special sign at the bottom. However, my sign may have a nonempty PHON value. I will introduce a feature called GAPTYPE which is a NONLOCAL feature whose value can be either trace or rp. I will introduce two constraints to capture the pattern of distribution of RPs and traces. At the top of the dependency, I will bind the nonempty SLASH at the complementizer point. I will propose a lexical entry for the complementizer ke that will account for the binding of SLASH by the feature BIND, which has a nonempty set as value.