Hagoromo Fulltouch Chalk is highly coveted around the world by mathematicians, who say it’s superior to other kinds of chalk because it has an almost buttery texture and erases easily. When Hagoromo announced it was ceasing production, many mathematicians bought lifetime supplies, like one professor who has a four-stick-a-day habit. But a Korean company bought Hagoromo and has faithfully reproduced the original recipe so there is no longer a need to stockpile it. It’s sometimes available on Amazon from third-party resellers.