@book{Jacobson, author = {Jacobson, E.}, title = {You must Relax. A Practical Method of Reducing the Strains of Modern Living, New York and London (Whittlesey House - McGraw-Hill Book Company) 1934.}, language = {en} } @book{Jacobson, author = {Jacobson, E.}, title = {Progressive relaxation, Chicago (The University of Chicago Press) 1959.}, language = {en} }