A simple proof of cut elimination for a intuitionistic sequent calculus. The calculus has 5 connectives: implication, conjunction, disjunction, true, and false.
logic.elf formalizes the syntax and typing judgment for the
cut.elf proves cut elimination. Note that this is an
extrinsic cast of the logic rather than the intrinsic version found on
the Twelf wiki. Read the code for
cut for a gist of how the proof
of/cut (the actual theorem) for the gory details.