Ed Southall is a teacher trainer at Huddersfield University in the UK, and the author of Yes But Why? Teaching for Understanding in Mathematics. Ed has taught mathematics for 14 years in secondary schools both in the UK and the Middle East. He has developed a large following online as @solvemymaths on twitter where he regularly posts mathematical puzzles. Vincent Pantaloni is a French mathematics high school teacher since 2000. He teaches in Orleans in French but also in English to the European and International Sections. With these students he has developed a teaching based on cooperative problem solving. He believes that searching and sharing strategies for complex problems in teamwork helps students in building a stronger mathematical knowledge. He is also a teacher trainer specialised in the use of new technologies and flipped classroom and a member of different research groups. He posts about mathematics on twitter @panlepan and in French on his website Mathzani.