Ah, yes. I remember the time when I saw someone write something vaguely like the following [0,ξ[={x|0<=x<ξ} Which was fun trying to figure out when written in

Ah, yes. I remember the time when I saw someone write something vaguely like the following [0,ξ[={x|0<=x<ξ} Which was fun trying to figure out when written in handwriting where ξ,{,} all look the same. If you can't figure out what it's supposed to be, this equation starts with a half-open interval denoted: [ξ,0[. This notation has some advantages but can be make things hard to read.