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_10 for which if x_10 were a lawyer, then x_10 is writing a letter. For all x_10, if x_10 writes a letter, then x_10 is making tea. For all x_10, if x_10 makes tea, then x_10 is a lawyer. For all x_10, if x_10 were a lawyer, then x_10 is making tea.
For all x_10, if x_10 writes a letter, then x_10 is a lawyer can be inferred via the universal transitivity rule. There is at least one x_10 for which if x_10 were a lawyer, then x_10 is making tea can be inferred via the existential transitivity rule. There is at least one x_10 for which if x_10 makes tea, then x_10 is writing a letter can be inferred via the existential transitivity rule. For all x_10, x_10 will make tea if and only if x_10 is a lawyer can be inferred via the universal biconditional introduction rule. For all x_10, x_10 is a lawyer if and only if x_10 will make tea can be inferred via the universal biconditional introduction rule.