Published online by Cambridge University Press: 12 March 2014
In [1] S. Buss introduced systems of bounded arithmetic ,
,
,
(i = 1, 2, 3, …).
and
are first order systems and
and
are second order systems.
and
are closely related to
and
respectively in the polynomial hierarchy, and
and
are closely related to PSPACE and EXPTIME respectively. One of the most important problems in bounded arithmetic is whether the hierarchy of bounded arithmetic collapses, i.e. whether
=
or
=
for some i, or whether
=
, or whether
is a conservative extension of S 2 = ⋃i
. These problems are relevant to the problems whether the polynomial hierarchy PH collapses or whether PSPACE = PH or whether PSPACE = EXPTIME. It was shown in [4] that
=
implies
and consequently the collapse of the polynomial hierarchy. We believe that the separation problems of bounded arithmetic and the separation problems of computational complexities are essentially the same problem, and the solution of one of them will lead to the solution of the other.