N ⊨ ψ ( n ) ⟺ n {\displaystyle {\mathcal {N}}\models \psi (n)\iff n} is irreducible.
N ⊨ ψ ( n ) ⟺ n {\displaystyle {\mathcal {N}}\models \psi (n)\iff n} δεν ανάγεται.