I want to know the answer to the following question:
In what year did William IV adopt a purity law pertaining to beer?
All the background I'm provided with is that "In 1516, William IV, Duke of Bavaria, adopted the Reinheitsgebot (purity law), perhaps the oldest food-quality regulation still in use in the 21st century, according to which the only allowed ingredients of beer are water, hops and barley-malt.". Is that enough to answer the question?
Answer: yes