 agents, however abstractly and partially given at this stage of
description.  The symbols of a formal system like {L(A), L(B)} can be held
subject to abstract constraints, having their meanings in relation to each
other determined by definitions and axioms, for example, the laws defining
an equivalence relation, making it possible to manipulate the resulting
information by means of the inference rules in a logical proof system.
This illustrates the &quot;proof-theoretic&quot; aspect of a symbol system.

Su