  Motivated by twisted N=4 supersymmetric Yang-Mills theory in 4 dimensions, a
natural extension of the monad (ADHM) construction relevant to D-instantons is
considered. We show that a family of Yang-Mills instantons can be constructed
from D-instantons. We discuss some possible roles of reciprocity in D-brane
physics. We conjecture the existence of universal instantons together with a
generalized Fourier-Nahm transformation as an unifying framework of D-brane
physics.
