<p class="noindent"> Every module in a Haskell program must be <span 
class="ptmri7t-">closed</span>. That is, every name explicitly mentioned by the
source code must be either defined locally or imported from another module. However, entities that the
compiler requires for type checking or other compile time analysis need not be imported if they are
not mentioned by name. The Haskell compilation system is responsible for finding any information
needed for compilation without the help of the programmer. Tha