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_2, if x_2 were a mechanic, then x_2 is reading a book. There is at least one x_2 for which x_2 is not a mechanic. For all x_2, if x_2 reads a book, then x_2 is writing a letter. For all x_2, if x_2 writes a letter, then x_2 is a mechanic.
There is at least one x_2 for which x_2 will not write a letter can be inferred via the existential modus tollens rule. For all x_2, if x_2 were a mechanic, then x_2 is writing a letter can be inferred via the universal transitivity rule. For all x_2, if x_2 reads a book, then x_2 is a mechanic can be inferred via the universal transitivity rule. For all x_2, if x_2 writes a letter, then x_2 is reading a book can be inferred via the universal transitivity rule.