require 'minitest/autorun'
 
f=->n{r=a=[]
(0...n).map{|i|a<<a=[i]}
r[0]||r}
 
 
describe '#f' do
  it 'returns the correct results' do
    assert_equal f[0], []
    assert_equal f[1], [0]
    assert_equal f[2], [0, [1]]
    assert_equal f[6], [0, [1, [2, [3, [4, [5]]]]]]
    assert_equal f[26], [0, [1, [2, [3, [4, [5, [6, [7, [8, [9, [10, [11, [12, [13, [14, [15, [16, [17, [18, [19, [20, [21, [22, [23, [24, [25]]]]]]]]]]]]]]]]]]]]]]]]]]
    assert_equal f[69], [0, [1, [2, [3, [4, [5, [6, [7, [8, [9, [10, [11, [12, [13, [14, [15, [16, [17, [18, [19, [20, [21, [22, [23, [24, [25, [26, [27, [28, [29, [30, [31, [32, [33, [34, [35, [36, [37, [38, [39, [40, [41, [42, [43, [44, [45, [46, [47, [48, [49, [50, [51, [52, [53, [54, [55, [56, [57, [58, [59, [60, [61, [62, [63, [64, [65, [66, [67, [68]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]
  end
end

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