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_10, if x_10 makes tea, then x_10 is sad. There is at least one x_10 for which x_10 is happy or x_10 will not make tea. For all x_10, if x_10 were sad, then x_10 is making tea.
There is at least one x_10 for which if x_10 makes tea, then x_10 is happy can be inferred via the existential rewriting rule. For all x_10, x_10 will make tea if and only if x_10 is sad can be inferred via the universal biconditional introduction rule. For all x_10, x_10 is sad if and only if x_10 will make tea can be inferred via the universal biconditional introduction rule.