Comment by bmacho

Off: mathematics is kind of moving away from the asymmetric element symbol "∈" to the symmetric type of symbol ":", which, I think is a loss. I'm sad about it.

For example with the element symbol you can do

   let x \in R a real number

and you also can do

   let U \subset R, U \ni 0 a neighborhood around 0 

Which you can't do with the type of symbol. I'm probably more picky about the notations following the sound in my head than the rest, but I still think that an asymmetric typeof symbol would be a net win.