I think it would be a healing ritual for the MO community for someone of appropriate stature (which excludes me) posting an inviting *cwiki* question that elicits responses from the users to this significant passing, the equivalent to mathematics of Bill Thurston's untimely death. The (useful) notice, [Grothendieck -sad news](https://mathoverflow.net/q/187106/6094), doesn't quite achieve it. Perhaps something along the lines of Dave Roberts' query in the comments...?