[Haskell-beginners] Understanding type variables in Haskell class declarations

[PATRICK BROWNE]

I am trying to understand how to interpret  type variables in Haskell class
declarations from a paper
<http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=1EA31D76684217BC728F916144BC6C38?doi=10.1.1.109.6853&rep=rep1&type=pdf>
.
With respect to the code below I have the following questions:
1. What is the difference between "a b" in the header of the Container
class and "a b" in the signature of the class methods? Does the whitespace
in header mean 2 distinct types and in the methods mean function
application?
2. In the Boathouse class what is the difference between the first ocurance
of "b p" and the second bracketed "(b p)"?
3. When I try to make instance of these classes I seem to need
FlexibleInstances. Why is this?



{-# LANGUAGE MultiParamTypeClasses #-}
-- Containers a b stands for all container types a holding things of type b.
-- from :info command a has kind *->*, b has kind *
class Containers a b where
 insert :: b -> a b -> a b
 remove :: b -> a b -> a b
 whatsIn :: a b -> [b]


class Surfaces a b where
 put :: b -> a b -> a b
 takeOff :: b -> a b -> a b
 whatsOn :: a b -> [b]

-- from :info command  "p" has kind  *, "h" and "b" have kind *->*
class People p
class Containers h p => Houses h p where
class (People p, Surfaces h p) => Boats h p where
class (Boats b p,Houses h (b p)) => BoatHouses h b p  where
class (People p, Houses h (b p),Boats b p) => HouseBoats h b p

-- 


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