Consider the following premises. There is at least one x_9 for which x_9 is excited if and only if x_9 will climb a mountain. For all x_9, x_9 will climb a mountain if and only if x_9 is excited. Can we infer the following from them? If we can, name the inference rule being used: For all x_9, if is not true that x_9 will climb a mountain if and only if x_9 is excited.
That contradicts the premises. Therefore the answer is no.