https://www.cleverism.com/servant-leadership-guide/
https://online.stu.edu/servant-leadership/
http://www.zingtrain.com/content/servant-leadership
https://yali.state.gov/courses/servant-leadership-3/
https://apscomunicacioenpublic.files.wordpress.com/2012/12/larry-spears-practicing-servant-leadership.pdf
https://www.regent.edu/acad/global/publications/jvl/vol1_iss1/Spears_Final.pdf