@XanderHenderson no, I just saw numerous flags like this and I hope that this message will make it stop. I could have written mod message instead but went for a more lowkey way at first.
@TheSimpliFire I've downvoted. Upon 3 net downvotes, it can be deleted for users with high enough rep. I think it is deletable for 10K users in two days. I've pinned the question in the side bar to the right.
@XanderHenderson What of learned from HNQ: If you really want to learn about the content of a site: Turn a blind eye to any HNQ's originating from that site. Based solely on my experience on MSE (likely a phenomenon wider than just MSE).
I really should propose a sociological study of HNQ's on MSE, in the context of SE. I'll talk to my colleagues about it ;-) (Oh trust me, a sociologist/social psychologist could write a book based on this site, and a book series on SE!!)
This question is, I think, overly broad and not very clear. I think that the right answer is "Please use Google to spend some time learning about non-constructive proofs," but I am not sure that this is exactly what the asker is looking for...
Oi... another user has approved the edit I pointed out above. Yikes...
Oh, hey... it is the same user who thinks that too many high quality questions are on the VLQ review queue.