(mixin (interface-expr ...) (interface-expr ...) class-clause ...)
The given class must implement interfaces produced by the first set of interface-exprs. The result of the procedure is a subclass of the given class that implements the interfaces produced by the second set of interface-exprs. The class-clauses are as for class*, to define the class extension encapsulated by the mixin.
Evaluation of a mixin form checks that the class-clauses are consistent with both sets of interface-exprs.