i
fatal DDH ()


fatal

illustration%20of%20%20%22unsolvable%20and%20undecidable%20problem%20which%20leads%20to%20madness%22%2C%20black%20background

illustration of "unsolvable and undecidable problem which leads to madness", black background

Problem P is "fatal" if no proof could ever be provided whether P is solvable or unsolvable. 

It is impossible to tell about problem if it is "fatal". That's why it is fatal ;)