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_4, if x_4 were an artist, then x_4 is making tea. There is at least one x_4 for which x_4 is sad if and only if x_4 will make tea. For all x_4, if x_4 makes tea, then x_4 is an artist.
For all x_4, x_4 is an artist if and only if x_4 will make tea can be inferred via the universal biconditional introduction rule. For all x_4, x_4 will make tea if and only if x_4 is an artist can be inferred via the universal biconditional introduction rule. There is at least one x_4 for which if x_4 were sad, then x_4 is making tea can be inferred via the existential biconditional elimination rule. There is at least one x_4 for which if x_4 makes tea, then x_4 is sad can be inferred via the existential biconditional elimination rule.