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: It is windy if and only if John is writing a letter. For all x, x will climb a mountain. It is not windy.
If it is windy, then John is writing a letter can be inferred via the biconditional elimination rule. If John writes a letter, then it is windy can be inferred via the biconditional elimination rule. John is not writing a letter can be inferred via the biconditional elimination rule.