A final postscript in my response to Paul C. concerning the notion
that exchange "expresses something equal": an additional indication
that the equivalence relation established by exchange does not
establish a relation of equality in the sense required by Marx is the
point, carried forward from my exchange with Fred, that absent
special assumptions about market conditions, the relationship is not
transitive. That is, in general the fact that A exchanges for B and
B exchanges for C does not imply that A is or can be exchanged for C.
But transitivity is a necessary condition for equality.
Gil Skillman