Consider the following premises. For all y, if y were curious, then y is writing a letter. If it is sunny, then John is not writing a letter. John is curious. Can we infer the following from them? It is sunny.
 From the fact that for all y, if y were curious, then y is writing a letter we can infer that if John were curious, then John is writing a letter. From the fact that if John were curious, then John is writing a letter, and that John is curious we can infer that John is writing a letter. Finally, from the fact that if it is sunny, then John is not writing a letter, and that John is writing a letter we can infer that it is not sunny, which contradicts that It is sunny. Therefore, the answer is no.