atKey allows you to access one key in another Pattern, i.e. PatternProxy (e.g. Pdef), Pbind and Pchain.
s.boot; Pdef( \one, Pbind( \degree, Pseq( (1..7), inf ), \dur, 1, \pan,-1 ) ); Pdef( \two, Pbind( \degree, Pdef(\one).atKey(\degree), \dur, 1, \pan, 1) ); Pdef( \one ).play; Pdef( \two ).play; // now change the first one: Pdef( \one, Pbind( \degree, Pseq( [1,3,5,7,5,3], inf ), \dur, 1, \pan, -1) ) ); // the second one still has the previous pattern Pdef( \two, Pbind( \degree, Pdef(\one).atKey(\degree), \dur, 1, \pan, 1 ) ); // now it has the same pattern at one again Pdef( \one).stop; Pdef( \two).stop;