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: There is at least one y for which if y were a server, then y is sad. For all y, if y were sad, then y is a server.
There is at least one y for which y is a server if and only if y is sad can be inferred via the existential biconditional introduction rule. There is at least one y for which y is sad if and only if y is a server can be inferred via the existential biconditional introduction rule.