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_15, if x_15 plays tennis, then x_15 is bored. For all x_15, if x_15 were bored, then x_15 is a sailor. For all x_15, x_15 will read a book if and only if x_15 will play tennis. There is at least one x_15 for which if x_15 were a sailor, then x_15 is reading a book.
For all x_15, if x_15 plays tennis, then x_15 is a sailor can be inferred via the universal transitivity rule. There is at least one x_15 for which if x_15 were bored, then x_15 is reading a book can be inferred via the existential transitivity rule. For all x_15, if x_15 reads a book, then x_15 is playing tennis can be inferred via the universal biconditional elimination rule. For all x_15, if x_15 plays tennis, then x_15 is reading a book can be inferred via the universal biconditional elimination rule.