  We present a new syntactical proof that first-order Peano Arithmetic with
Skolem axioms is conservative over Peano Arithmetic alone for arithmetical
formulas. This result - which shows that the Excluded Middle principle can be
used to eliminate Skolem functions - has been previously proved by other
techniques, among them the epsilon substitution method and forcing. In our
proof, we employ Interactive Realizability, a computational semantics for Peano
Arithmetic which extends Kreisel's modified realizability to the classical
case.
