Abstract: 
We derive 4dimensional N=4 U(N) supersymmetric YangMills theory
from a 3dimensional ChernSimonsmatter theory
with product gauge group (U(N))^{2n}.
The latter describes M2branes probing an orbifold where
a torus emerges in a scaling limit. Starting from
one single ChernSimonsmatter theory, we find infinitely
many equivalent 4dimensional theories differing up to
SL(2,Z) redefinition of the gauge coupling tau (= theta/2pi + 4pi i/g2).
This would provide a proof of the MontonenOlive duality.
However, because our tau is not generic,
the Stransformation (tau > tau^{1}) can be thought of
as a parity transformation in 4 dimensions.
