B. Woltzenlogel-Paleo et al.:
"All about Proofs, Proofs for All";
in series "Mathematical Logic and Foundations", series editor: B. Woltzenlogel-Paleo et al.; College Publications, 2015, ISBN: 978-1-84890-166-7.
http://www.collegepublications.co.uk/logic/mlf/?00023