Making Array#uniq work

OK, according to the Pickaxe 2nd. Edition, Array#uniq judges uniqueness based on eql?. Somehow this doesn't seem to work for me :).
Following code returns the Array with two members instead of the one I would wish for. Any pointers? I'm running 1.8.2

class A
   attr_accessor :a,:b
   def initialize a
     @a=a
     @b=Array.new
   end
   def << item
     @b<<item
   end
  
   def eql? other
     return true if @a==other.a && @b==other.b
   end
   def == other
     return eql?(other)
   end
end

o1=A.new("a")
o2=A.new("a")
o1<<"o"
o2<<"o"
puts o1==o2
puts o1.eql?(o2)
p [o1,o2].uniq

···

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