(\x.x)
\x.\y.x
(x
x
(\f.\g.\x.(g(f(x))))
(\x. x x)    
(\x.x) (\x.x)
(\id. id id) (\x.x)
let id = \x.x in id id 
\x. let f = x in f f      
fix (\x.x)
fix unit
\x. unit (unit x)
fix (\x. append (unit x))
\x. fix (\xs. append (unit x) xs)
let id = \x.x in id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id id