  The purpose of this paper is to identify programs with control operators
whose reduction semantics are in exact correspondence. This is achieved by
introducing a relation $\simeq$, defined over a revised presentation of
Parigot's $\lambda\mu$-calculus we dub $\Lambda M$. Our result builds on two
fundamental ingredients: (1) factorization of $\lambda\mu$-reduction into
multiplicative and exponential steps by means of explicit term operators of
$\Lambda M$, and (2) translation of $\Lambda M$-terms into Laurent's polarized
proof-nets (PPN) such that cut-elimination in PPN simulates our calculus. Our
proposed relation $\simeq$ is shown to characterize structural equivalence in
PPN. Most notably, $\simeq$ is shown to be a strong bisimulation with respect
to reduction in $\Lambda M$, i.e. two $\simeq$-equivalent terms have the exact
same reduction semantics, a result which fails for Regnier's
$\sigma$-equivalence in $\lambda$-calculus as well as for Laurent's
$\sigma$-equivalence in $\lambda\mu$.
