  It is shown that Tarski's set of ten axioms for the calculus of relations is
independent in the sense that no axiom can be derived from the remaining
axioms. It is also shown that by modifying one of Tarski's axioms slightly, and
in fact by replacing the right-hand distributive law for relative
multiplication with its left-hand version, we arrive at an equivalent set of
axioms which is redundant in the sense that one of the axioms, namely the
second involution law, is derivable from the other axioms. The set of remaining
axioms is independent. Finally, it is shown that if both the left-hand and
right-hand distributive laws for relative multiplication are included in the
set of axioms, then two of Tarski's other axioms become redundant, namely the
second involution law and the distributive law for converse. The set of
remaining axioms is independent and equivalent to Tarski's axiom system.
