Refinement symbol

[barrucadu]

There are two problems with the current syntax:

1. -[- is not a valid Haskell operator name, because someone could do this:

instance Num a => Num [a] where
    fromIntegral n = [fromInteger n]
    a - b = [sum a - sum b]
  ...

> 3 -[- 6 ]
 9

2. The real operator is actually read as "is refined by", not "refines". So it's backwards.