  We explore maximally supersymmetric Yang-Mills theory with walls of
impurities respecting half of the supersymmetries. The walls carry fundamental
or bifundamental matter multiplets. We employ three-dimensional N=2 superspace
language to identify the Higgs branch of this theory. We find that the vacuum
conditions determining the Higgs branch are exactly the bow equations yielding
Yang-Mills instantons on a multi-Taub-NUT space.
  Under electric-magnetic duality, the super Yang-Mills theory describing the
bulk is mapped to itself, while the fundamental- and bifundamental-carrying
impurity walls are interchanged. We perform a one-loop computation on the
Coulomb branch of the dual theory to find the asymptotic metric on the original
Higgs branch.
