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, x_1 will take a plane or x_1 will not write a letter. There is at least one x_1 for which x_1 will write a letter. For all x_1, x_1 is a doctor.
There is at least one x_1 for which x_1 will write a letter and x_1 is a doctor can be inferred via the existential conjunction rule. Some doctors will write a letter can be inferred via the existential conjunction rule. For all x_1, if x_1 writes a letter, then x_1 is taking a plane can be inferred via the universal rewriting rule.