u/RandomHannah48

Asking for my brother, I don't know much myself, this might be more advanced, but my brother said the top left was a famous shape called the carpenter's square and he knew it had a ko in it. He said he was going to play A, but instead chose 1 and 3, he felt like a genius grabbing a stone and ending all possible life and death problems with the famous top left shape. But better players still pointed out that 1 and 3 were still mistakes. As for me, I only know you can't get a group killed in the opening, my brother also thinks if a ko happens in the opening there will not be enough ko threats.
Thanks!