What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Name the inference rule being used: For all x_3, if x_3 takes a plane, then x_3 is playing tennis. For all x_3, if x_3 reads a book, then x_3 is playing tennis. There is at least one x_3 for which x_3 is not sad or x_3 will read a book. For all x_3, x_3 is sad or x_3 will take a plane.
There is at least one x_3 for which x_3 will take a plane or x_3 will read a book can be inferred via the existential resolution rule.