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_15 for which if x_15 were an office clerk, then x_15 is curious. For all x_15, if x_15 were curious, then x_15 is making tea. For all x_15, x_15 is a mechanic if and only if x_15 will make tea. For all x_15, if x_15 were a mechanic, then x_15 is an office clerk.
There is at least one x_15 for which if x_15 were an office clerk, then x_15 is making tea can be inferred via the existential transitivity rule. There is at least one x_15 for which if x_15 were a mechanic, then x_15 is curious can be inferred via the existential transitivity rule. For all x_15, if x_15 were a mechanic, then x_15 is making tea can be inferred via the universal biconditional elimination rule. For all x_15, if x_15 makes tea, then x_15 is a mechanic can be inferred via the universal biconditional elimination rule.