-- Normal fixed point
fix f = f (fix f)

-- | Slow comonadic fixed point à la Kenneth Foner:
pfix :: Comonad w => w (w a -> a) -> w a
pfix = extend wfix

-- | Comonadic fixed point à la Kenneth Foner:
kfix :: ComonadApply w => w (w a -> a) -> w a
kfix w = fix $ \u -> w <@> duplicate u

-- | Comonadic fixed point à la Blom:
bfix :: ComonadApply w => w (w a -> a) -> w a
bfix w = w <@> extend bfix w