Thanks evebody for yours answers, helps a lot :) !

Jesús : looks fantastic, but could you give me fex explanation how it 
works?
> a = Hash.new {|h,k| h[k] = Hash.new(&h.default_proc)}

is this a way to override the method new for the object a?

You're doing so by passing the following block but then i'm lost, do you 
have any links to share which detail that ?

Nico (so much to learn...)
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