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: There is at least one x_7 for which x_7 will write a letter if and only if x_7 will make tea. For all x_7, if x_7 sleeps, then x_7 is writing a letter. For all x_7, x_7 will make tea.
There is at least one x_7 for which if x_7 writes a letter, then x_7 is making tea can be inferred via the existential biconditional elimination rule. There is at least one x_7 for which if x_7 makes tea, then x_7 is writing a letter can be inferred via the existential biconditional elimination rule.