Consider the following premises. Richard is playing squash if and only if David is an office clerk. For all x_17, if x_17 takes a plane, then x_17 is playing squash. If David were an office clerk, then Richard is taking a plane. Can we infer the following from them? If we can, name the inference rule being used: The fact that David were an office clerk does not imply that Richard is playing squash.
That contradicts the premises. Therefore the answer is no.