Contractive idempotents on locally compact quantum groups Matthias NeufangPekka SalmiAdam SkalskiNico Spronk Primary 46L65Secondary 43A0546L3060B15Locally compact quantum groupcontractive idempotent functionalternary ring of operators A general form of contractive idempotent functionals on coamenable locally compact quantum groups is obtained, generalising the result of Greenleaf on contractive measures on locally compact groups. The image of a convolution operator associated with a contractive idempotent is shown to be a ternary ring of operators. As a consequence, a one-to-one correspondence between contractive idempotents and a certain class of ternary rings of operators is established. Indiana University Mathematics Journal 2013 text pdf 10.1512/iumj.2013.62.5178 10.1512/iumj.2013.62.5178 en Indiana Univ. Math. J. 62 (2013) 1983 - 2002 state-of-the-art mathematics http://iumj.org/access/