The aim of the present paper is to provide a
formula for the ε - subdifferential of f + g o h
different from the ones which can be found in the existent
literature. Further we equivalently characterize this formula by
using of a so-called closedness type regularity condition
expressed by means of the epigraphs of the conjugates of the
functions involved. Even more, using the ε - subdifferential
formula we are able to derive necessary and sufficient conditions
for the ε - optimal solutions of composed convex optimization
problems.