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_13, if x_13 were a mechanic, then x_13 is drinking water. For all x_13, if x_13 drinks water, then x_13 is a mechanic. Karen is not sad. Karen is sad if and only if Thomas is a mechanic.
If Karen were sad, then Thomas is a mechanic can be inferred via the biconditional elimination rule. If Thomas were a mechanic, then Karen is sad can be inferred via the biconditional elimination rule. Thomas is not a mechanic can be inferred via the biconditional elimination rule. For all x_13, x_13 is a mechanic if and only if x_13 will drink water can be inferred via the universal biconditional introduction rule. For all x_13, x_13 will drink water if and only if x_13 is a mechanic can be inferred via the universal biconditional introduction rule.