The next three exercises contain arguments from a single set of premises. In each case decide whether or not the argument is valid. If it is, give an informal proof. If it isnt, use Tarskis World to construct a counterexample.

12.18 1 |vxvy [Leftof(x, y) | Larger(x,y)l )] yx Cube(x) Small(x) tx Tet(x) Large(x)] yx Vy (Small(x) Small (y)) -Larger(x, y)] Vz yw/(Tet (z) Cube(w) ) LeftO(z, w)] 12.18 1 |vxvy [Leftof(x, y) | Larger(x,y)l )] yx Cube(x) Small(x) tx Tet(x) Large(x)] yx Vy (Small(x) Small (y)) -Larger(x, y)] Vz yw/(Tet (z) Cube(w) ) LeftO(z, w)]