@incollection{AST_1973__7-8__223_0,
     author = {Popp, Herbert},
     title = {Introduction to the algebraic theory of fundamental groups},
     booktitle = {Singularit\'es \`a Carg\`ese},
     series = {Ast\'erisque},
     pages = {223--240},
     publisher = {Soci\'et\'e math\'ematique de France},
     number = {7-8},
     year = {1973},
     mrnumber = {401763},
     zbl = {0295.14013},
     language = {en},
     url = {http://archive.numdam.org/item/AST_1973__7-8__223_0/}
}