  Interface theories are powerful frameworks supporting incremental and
compositional design of systems through refinements and constructs for
conjunction, and parallel composition. In this report we present a first
Interface Theor -- |Modal Mixed Interfaces -- for systems exhibiting both
non-determinism and randomness in their behaviour. The associated component
model -- Mixed Markov Decision Processes -- is also novel and subsumes both
ordinary Markov Decision Processes and Probabilistic Automata.
