Q on associative binary operation

hi, how do we complete this table Table shown may be completed to define 'associative' binary operation * on S={a,b,c,d}. Assume this is possible and compute the missing entries *|a|b|c|d --------- a|a|b|c|d --------- b|b|a|c|d --------- c|c|d|c|d --------- d| | | | Its clear for commutativity but I am a trifle confused on how we do it for associativity. Thank you. Regards Sarath. __________________________________ Do you Yahoo!? Yahoo! SiteBuilder - Free, easy-to-use web site design software http://sitebuilder.yahoo.com