A class B is behaviorally compatible with class A with respect to
a generic projection function p if for all messages m which a}i activate
a method attached to B

(p (m args)) = (apply 'm (mapcar p (list args)))

mapcar applies the projection }ifunction to all arguments of m
and returns the list of projections.}i
p is the identity for most classes

Example:
LabeledEdge = *inherit* Edge <label> Number.

Class LabeledEdge is behaviorally compatible with class Edge with
respect to the projection function which is the identity for all classes,
except LabeledEdge. For this class, the projection fu{yncton maps
a labeled edge into an edge by dropping the lab}iel.

(source-node iLabeledEdge) = source}i-node iEdge)

Assume that the edges are directed and that method source-node
returns the source node. }i{_}i}i}i

If a class B inherits with}i override from a class A then B is
behaviorally compatible with class A{_ with respect to the following
projection function:}i from this inherit
union projections from}i subtypes.