  The formal system lambda-delta is a typed lambda calculus that pursues the
unification of terms, types, environments and contexts as the main goal.
lambda-delta takes some features from the Automath-related lambda calculi and
some from the pure type systems, but differs from both in that it does not
include the Pi construction while it provides for an abbreviation mechanism at
the level of terms. lambda-delta enjoys some important desirable properties
such as the confluence of reduction, the correctness of types, the uniqueness
of types up to conversion, the subject reduction of the type assignment, the
strong normalization of the typed terms and, as a corollary, the decidability
of type inference problem.
