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_12, x_12 is a cashier or x_12 will play squash. There is at least one x_12 for which if x_12 plays squash, then x_12 is a mechanic. For all x_12, if x_12 were a cashier, then x_12 is a mechanic. For all x_12, x_12 is a mechanic if and only if x_12 is fast.
There is at least one x_12 for which x_12 is a mechanic can be inferred via the existential disjunction elimination rule. For all x_12, if x_12 were a mechanic, then x_12 is fast can be inferred via the universal biconditional elimination rule. For all x_12, if x_12 were fast, then x_12 is a mechanic can be inferred via the universal biconditional elimination rule.