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: Charles is not curious. Barbara is writing a letter if and only if Jennifer is excited. For all x_7, x_7 is sad if and only if x_7 will write a letter. If Jennifer were excited, then it is snowing. Charles is curious if and only if it is snowing.
If Barbara writes a letter, then Jennifer is excited can be inferred via the biconditional elimination rule. If Charles were curious, then it is snowing can be inferred via the biconditional elimination rule. If Jennifer were excited, then Barbara is writing a letter can be inferred via the biconditional elimination rule. If it snows, then Charles is curious can be inferred via the biconditional elimination rule. It is not snowing can be inferred via the biconditional elimination rule. For all x_7, if x_7 were sad, then x_7 is writing a letter can be inferred via the universal biconditional elimination rule. For all x_7, if x_7 writes a letter, then x_7 is sad can be inferred via the universal biconditional elimination rule.