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PiSigma is a small dependently typed language with only very few
constructs: Type:Type, Pi-types, Sigma-types, enumerations and a
general meachanism for mutual recursion for types and values
controlled by lifted types. It is intended as a core language for
dependently typed languages like Agda. It has been described in the
paper emPiSigma: Dependent Types Without the Sugar/em which has
appeared in the proceedings of FLOPS 2010.