Undecidability of Equality in the Free Locally Cartesian Closed Category

We show that a version of Martin-Löf type theory with extensional identity, a unit type N1,Σ,Π, and a base type is a free category with families (supporting these type formers) both in a 1and a 2-categorical sense. It follows that the underlying category of contexts is a free locally cartesian closed category in a 2-categorical sense because of a previously proved biequivalence. We then show that equality in this category is undecidable by reducing it to the undecidability of convertibility in combinatory logic.