Consider the following premises. It is not snowing. For all x_20, x_20 will not go running. For all x_20, x_20 will go running or x_20 is a scientist. It is snowing or Mary is writing a letter. Can we infer the following from them? Mary is not writing a letter.
 From the fact that for all x_20, x_20 will go running or x_20 is a scientist, and that for all x_20, x_20 will not go running we can infer that for all x_20, x_20 is a scientist. Finally, from the fact that it is snowing or Mary is writing a letter, and that it is not snowing we can infer that Mary is writing a letter, which contradicts that Mary is not writing a letter. Therefore, the answer is no.