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_1, if x_1 takes a plane, then x_1 is listening to a song. For all x_1, if x_1 were excited, then x_1 is listening to a song. There is at least one x_1 for which if x_1 writes a letter, then x_1 is excited. For all x_1, x_1 will write a letter or x_1 will take a plane.
There is at least one x_1 for which if x_1 writes a letter, then x_1 is listening to a song can be inferred via the existential transitivity rule.