Alternatives to NOT-1 are ( ϕ → ¬ χ ) → ( χ → ¬ ϕ ) {\displaystyle (\phi \to \lnot \chi )\to (\chi \to \lnot \phi )} or ( ϕ → ¬ ϕ ) → ¬ ϕ {\displaystyle (\phi \to \lnot \phi )\to \lnot \phi } .
Альтернативи НЕ-1 ( ϕ → ¬ χ ) → ( χ → ¬ ϕ ) {\displaystyle (\phi \to \lnot \chi )\to (\chi \to \lnot \phi )} або ( ϕ → ¬ ϕ ) → ¬ ϕ {\displaystyle (\phi \to \lnot \phi )\to \lnot \phi } .