Questions tagged [p-hardness]

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proof that 2-SAT is P-hard [closed]

i'm doing university work about the 2-sat problem and it is asked why 2-sat is p-hard. We discussed that 3-sat is np-hard and proved this by reduction from cnf-sat to 3cnf-sat. for my work the ...
6 votes
1 answer
282 views

What is the complexity of HORN-2CNF entailment?

I know the entailment of a propositional variable in a HORN-3CNF formula is $P$-complete. I can't find any publication in which it has been shown the complexity of the same problem for HORN-2CNF ...
1 vote
1 answer
128 views

Recursively presenting or even enumerating all P-hard languages

A class of languages $C$ is recursively presentable if there is an effective enumeration of Turing machines $\mathcal{M}_1,\mathcal{M}_2,\ldots$ such that $C=\{L(\mathcal{M}_i)\mid i=1,2,\ldots\}$. ...
14 votes
4 answers
726 views

P-complete problems on trees

This question is related to one of my previous questions, NP-hard problems on trees. I am looking for problems that are P-complete on trees.
41 votes
2 answers
2k views

Are the problems PRIMES, FACTORING known to be P-hard?

Let PRIMES (a.k.a. primality testing) be the problem: Given a natural number $n$, is $n$ a prime number? Let FACTORING be the problem: Given natural numbers $n$, $m$ with $1 \leq m \leq n$, ...
11 votes
1 answer
298 views

Density of P-complete languages

Suppose $L$ is a Boolean language, of finite strings over $\{0,1\}$. Let $L_n$ be the number of strings in $L$ with length $n$. For a function $d(n)$ from the positive integers to the positive real ...