+
+ SETUP::
+
+ sage: from mjo.symbol_sequence import SymbolSequence
+
+ EXAMPLES::
+
+ sage: a = SymbolSequence('a')
+ sage: a._flatten_list_([1,2,3])
+ [1, 2, 3]
+ sage: a._flatten_list_([1,[2,3]])
+ [1, 2, 3]
+ sage: a._flatten_list_([1,[2,[3]]])
+ [1, 2, 3]
+ sage: a._flatten_list_([[[[[1,[2,[3]]]]]]])
+ [1, 2, 3]
+