Description: Stoic logic Thema 2 version a. Statement T2 of Bobzien p. 117 shows a
reconstructed version of Stoic logic thema 2 as follows: "When from two
assertibles a third follows, and from the third and one (or both) of the
two another follows, then this other follows from the first two."
Bobzien uses constructs such as ph , ps |- ch ; in Metamath we will
represent that construct as ph /\ ps -> ch . This version a is
without the phrase "or both"; see stoic2b for the version with the
phrase "or both". We already have this rule as syldan , so here we
show the equivalence and discourage its use.
(New usage is discouraged.)(Contributed by David A. Wheeler, 17-Feb-2019)