Q:

Incomparable NPI decision problems

Assume that there exists at least one NP-intermediate decision problem (which, by Ladner's theorem, is equivalent to P being distinct from NP).
Do there exist two NP-intermediate decision problems, $A$ and $B$, such that neither one is polynomial-time reducible to the other?

A:

Balcazar and Diaz proved that if $P \ne NP$ then there exists an infinite number of non-comparable languages in $NP$.

