  The quotient operation, which is dual to the composition, is crucial in
specification theories as it allows the synthesis of missing specifications and
thus enables incremental design. In this paper, we consider a specification
theory based on marked acceptance specifications (MAS) which are automata
enriched with variability information encoded by acceptance sets and with
reachability constraints on states. We define a sound and complete quotient for
MAS hence ensuring reachability properties by construction.
