Take p.q &
q. When you write p.q in the
a–b notation,
it is impossible to see from the symbol alone that q follows
from it; for if you were to
substitute || interpret the
true-pole as the false, the same symbol
would stand for
p⌵q, from
which q doesn't
follow. But the moment you say
which symbols are tautologies, it
at once becomes possible to see from
the
fact, that they are & the original symbol that
q does follow.