  Notwithstanding interest and excitement building around quantum computing in
the last decades, a concise statement saying where this computing can truly
help is still missing. As it is shown in the present paper, equal cost of
computation for truth and falsity of experimental quantum propositions
(required in order to infer a conclusion from a premise) cannot be achieved
with classical computing. On the other hand, this equality might be realized
with quantum parallel computing provided that the efficiency of such computing
can be greater than 1.
