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_11, if x_11 were a taxi driver, then x_11 is a scientist. There is at least one x_11 for which x_11 is a taxi driver. For all x_11, x_11 is a carpenter if and only if x_11 will write a letter. For all x_11, if x_11 were a carpenter, then x_11 is not a scientist.
There is at least one x_11 for which x_11 is a scientist can be inferred via the existential modus ponens rule. For all x_11, if x_11 were a carpenter, then x_11 is writing a letter can be inferred via the universal biconditional elimination rule. For all x_11, if x_11 writes a letter, then x_11 is a carpenter can be inferred via the universal biconditional elimination rule.