Complex sentence: Semantic tableaux are a proof method for formal systems--cf. Gentzen's natural deduction and sequent calculus, or even J. Alan Robinson's resolution and Hilbert's axiomatic systems.
Split into simpler sentences: Semantic tableaux are a proof method for formal systems. Cf. Gentzen's natural deduction and sequent calculus, or even J. Alan Robinson's resolution and Hilbert's axiomatic systems.