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 writes a letter, then x_3 is sleeping. There is at least one x_3 for which x_3 will write a letter. For all x_3, if x_3 were a sailor, then x_3 is not sleeping.
There is at least one x_3 for which x_3 will sleep can be inferred via the existential modus ponens rule.