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, x is not a mechanic. For all x, x will drink water or x is a doctor. For all x, if x were a mechanic, then x is a doctor. For all x, if x were a doctor, then x is a mechanic. For all x, x will not drink water or x will write a letter.
For all x, x is not a doctor can be inferred via the universal modus tollens rule. For all x, x is a doctor or x will write a letter can be inferred via the universal resolution rule. For all x, x is a mechanic if and only if x is a doctor can be inferred via the universal biconditional introduction rule. For all x, x is a doctor if and only if x is a mechanic can be inferred via the universal biconditional introduction rule.