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The Monkey has swung home to find his tree all in pieces.
He likes order and scoops up all his 'tree-parts' and sets them out in 3 groups.
The Monkey's 3 nested lists:
STEP = [['S', '1', 'B', '3'], ['S', '3', 'B', '11'], ['S', '5', 'B', '12'], ['S', '4', 'B', '13'], ['S', '2', 'B', '14']]
TRA...