Schonemann's criterion

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For a polynomial q denote by $q^*$ the residue of $q$ modulo $p$. Suppose the following conditions hold:

  • $k=f^n+pg$ with $n\geq 1$, $p$ prime, and $f,g\in \mathbb{Z}[X]$.
  • $\text{deg}(f^n)>\text{deg}(g)$.
  • $k$ is primitive.
  • $f^*$ is irreducible in $\mathbb{F}_p[X]$.
  • $f^*$ does not divide $g^*$.

Then $k$ is irreducible in $\mathbb{Q}[X]$.

See also Eisenstein's criterion.