網址: https://d3i71xaburhd42.cloudfront.net/a9ed7dd0fa1da1da588a58e50d12f2c653835616/17-Figure5-1.png
網址2: https://www.semanticscholar.org/paper/The-flow-method-for-the-Baker-Campbell-Hausdorff-Zadra-Bravetti/a9ed7dd0fa1da1da588a58e50d12f2c653835616/figure/3
