(ADVISE1 @RTLIN @BEFORE @(RI X1 USED) @(PROG()(CLEAR)(FOR NEW X IN (CONS X1 USED) DO (LINE (NODE (CAAR X)) (NODE (PLUS (CAAR X) 20)) (NODE (CDAR X)) (NODE (PLUS (CDAR X) 20)))) (SHOW 4))))))))