Metamath Proof Explorer


Theorem mt3d

Description: Modus tollens deduction. (Contributed by NM, 26-Mar-1995)

Ref Expression
Hypotheses mt3d.1 φ ¬ χ
mt3d.2 φ ¬ ψ χ
Assertion mt3d φ ψ

Proof

Step Hyp Ref Expression
1 mt3d.1 φ ¬ χ
2 mt3d.2 φ ¬ ψ χ
3 2 con1d φ ¬ χ ψ
4 1 3 mpd φ ψ