Wang�s Method (Cont.)
Or on the left: X, A v B, Y => Z
becomes X, A, Y => Z; X, B, Y => Z.
And on the right: X => Y, A & B, Z
becomes X => Y, A, Z; X => Y, B, Z.
In a split, both of the new sequents must be proved.
Axiom: A sequent in which any proposition symbol
occurs at top level on both the left and right sides.