+ """Merge N dicts into one dict containing the union of all keys/values in
+ the input dicts. When keys collide, apply the aggregation_function which,
+ by default, creates a list of values. See also coalesce_by_creating_set or
+ provide a user defined aggregation_function.
+
+ >>> a = {'a': 1, 'b': 2}
+ >>> b = {'b': 1, 'c': 2, 'd': 3}
+ >>> c = {'c': 1, 'd': 2}
+ >>> coalesce([a, b, c])
+ {'a': 1, 'b': [1, 2], 'c': [1, 2], 'd': [2, 3]}
+
+ """