I was reading about about NP-intermediate problems on Wikipedia and saw the IMSAT problem mentioned over there.
There is no Wikipedia page for that problem and they only cite this paper.
In the paper they define the MSAT problem as:
Recall that the satisfiability problem (SAT) is to decide whether a set of propositional clauses $C = \{C_1, ... ,C_m\}$, where each $C_i$ is a set of literals, on atoms $X = \{x_1, ... , x_n \}$ is satisfied by some truth assignment to $X$. Its restriction $MSAT$, where every clause of $C$ must be either positive or negative, i.e., must not contain any negative or positive literal, respectively, is still NP-hard.
But they don't reference any source that prove $MSAT$ is indeed NP-Hard. Can you please enlighten me?
Moreover, they later introduce the problem of IMSAT by:
The first subcase of MSAT which we consider is made up of instances with the property that every pair of a positive clause and a negative clause resolves, i.e. there is an atoms which occurs unnegated in the positive and negated in the negative clause.
I don't understand why Wikipedia mentioned this problem as NP-intermediate, this term was never shown in the paper. I see they prove that co-IMSAT is TRANS-HYP-complete, but couldn'tunderstand if TRANS-HYP is NP-intermediate, and what does it say on IMSAT.
I got a mess here, and I couldn't find any other sources. Is MSAT NP-Hard? I would like to see a proof (or at least an idea for a proof) Is IMSAT NP-intermediate? A proof of that seems to be missing as well, or I totally didn't understand the paper.
And another a bit more general question about using NP-intermediate problems:
If I understand correctly, it is quiet impossible to prove something is in NP-intermediate, since the class is defined as problems that polynomial running time solution was not found for them, and they were not proven to be NP-Hard (though they are in NP). If I want to "lean" on IMSAT as NP-intermediate. how can I do that?
Lets say I have a reduction from IMSAT to my problem P, which means if P is solvable in polynomial time, IMSAT as well. What paper can I cite to show that IMSAT in NP-intermediate - which can convince people P is a hard problem (and it is fair to use approximate/probabilistic algorithm instead of trying to solve it)