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: Barbara is a server if and only if Mary is writing a letter. Barbara is a server or Linda is making tea. If Linda makes tea, then Mary is writing a letter.
If Barbara were a server, then Mary is writing a letter can be inferred via the biconditional elimination rule. If Mary writes a letter, then Barbara is a server can be inferred via the biconditional elimination rule.