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: Patricia is playing squash if and only if it is late. For all x_10, x_10 will not play squash. It is late or David is writing a letter.
If Patricia plays squash, then it is late can be inferred via the biconditional elimination rule. If it is late, then Patricia is playing squash can be inferred via the biconditional elimination rule.