Controlling interference in ambients

Two forms of interferences are individuated in Cardelli and Gordon's Mobile Ambients (MA): plain interferences, which are similar to the interferences one finds in CCS and φ-calculus; and grave interferences, which are more dangerous and may be regarded as programming errors. To control interferences, the MA movement primitives are modified. On the new calculus, the Mobile Safe Ambients (SA), a type system is defined that: controls the mobility of ambients; removes all grave interferences. Other advantages of SA are: a useful algebraic theory; programs sometimes more robust (they require milder conditions for correctness) and/or simpler. These points are illustrated on several examples.