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_8, x_8 is a sailor if and only if x_8 is a mechanic. There is at least one x_8 for which if x_8 writes a letter, then x_8 is a cashier. For all x_8, if x_8 were a cashier, then x_8 is a mechanic. For all x_8, x_8 will write a letter or x_8 is a sailor.
There is at least one x_8 for which if x_8 writes a letter, then x_8 is a mechanic can be inferred via the existential transitivity rule. For all x_8, if x_8 were a sailor, then x_8 is a mechanic can be inferred via the universal biconditional elimination rule. For all x_8, if x_8 were a mechanic, then x_8 is a sailor can be inferred via the universal biconditional elimination rule.