U+2208 ∈
U+2209 ∉
U+2211 ∑
U+221A √
U+2227 ∧
U+2228 ∨
U+2260 ≠
U+2261 ≡
U+2264 ≤
U+2265 ≥

more Geometric shapes (U+25A0 -> U+25FF)

http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#unicode-syntax

U+E000 - U+F000 is private area, add some fancy symbols:

* status of battery, sound volume, wifi signal
* logo of some software, websites
* use two custom symbols to represent double width characters

Use U+EE as prefix
