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_6, if x_6 were a mechanic, then x_6 is running. For all x_6, if x_6 writes a letter, then x_6 is playing tennis. For all x_6, if x_6 writes a letter, then x_6 is a mechanic. For all x_6, if x_6 goes running, then x_6 is writing a letter. For all x_6, x_6 will not play tennis.
For all x_6, x_6 will not write a letter can be inferred via the universal modus tollens rule. For all x_6, if x_6 were a mechanic, then x_6 is writing a letter can be inferred via the universal transitivity rule. For all x_6, if x_6 writes a letter, then x_6 is running can be inferred via the universal transitivity rule. For all x_6, if x_6 goes running, then x_6 is playing tennis can be inferred via the universal transitivity rule. For all x_6, if x_6 goes running, then x_6 is a mechanic can be inferred via the universal transitivity rule.