Some twentieth-century art is great art. All great art involves original ideas, and any art that is not influential ...

Hello, I got confused on the explanation (the key takeaway) when it states that if two conditionals have the same sufficient condition, we can combine them into a complex conditional with an OR sufficient condition, but shouldn’t it be with an AND necessary condition? And the statement that if two conditionals have the same necessary condition, I can combine them into a complex conditional with an AND necessary condition - is it not a OR sufficient condition instead? Could somebody explain this concept for me with examples? Thank you!