Metamath Proof Explorer

Theorem mt2

Description: A rule similar to modus tollens. Inference associated with con2i . (Contributed by NM, 19-Aug-1993) (Proof shortened by Wolf Lammen, 10-Sep-2013)

Ref Expression
Hypotheses mt2.1 ψ
mt2.2 φ ¬ ψ
Assertion mt2 ¬ φ


Step Hyp Ref Expression
1 mt2.1 ψ
2 mt2.2 φ ¬ ψ
3 1 a1i φ ψ
4 3 2 pm2.65i ¬ φ