Mark was a huge figure on "the applicability of mathematics", which wasn't really my thing. But his refined attention to the way mathematics is used, revealed to me a whole new world of richness, within the seemingly "elementary" mathematics of numbers - their addition and multiplication. My cognitive account of his view on that became the center piece of my PhD, which was reformed to revolve around it (even helping me make progress after getting stuck for years on my cognitive account of Russell's paradox, which I still haven't fully cracked).
I guess what I'm trying to say is, R.I.P.
And damn you Coronavirus, this is really starting to get personal
Taken from a post in Aviv's personal Facebook page: https://www.facebook.com/aviv.keren/posts/10157387576239624