Discussion. The control operators discussed here bear a strong resemblance to the syntactic control features used in Stabler's algebraic formulation of Minimalist Grammars (Stabler 1997, 1999). These features, like ◊,□, come in matching pairs of a licensor ‘+f’ and a licensee ‘−f’ that have to cancel for a derivation to be successful; movement is triggered by the presence of an appropriate licensor feature.  For an explicit comparison of the mimimalist and the typelogical view on structural control, see Vermaat (2004).