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_7, x_7 will write a letter. For all x_7, if x_7 were a police officer, then x_7 is a sailor. There is at least one x_7 for which if x_7 were a nurse, then x_7 is a sailor. For all x_7, x_7 is a nurse or x_7 is a police officer.
There is at least one x_7 for which x_7 is a sailor can be inferred via the existential disjunction elimination rule.