Classic Qi system (Qi et al. 2005) — dx/dt = a·(y − x) + y·z, dy/dt = c·x − y − x·z, dz/dt = x·y − b·z. Classic chaotic a=35 b=8/3 c=25 (b fixed). Dual a+c sliders. Distinct from four-wing Qi (fourwing.html), Yu–Wang (yu-wang.html), Liu (liu.html), Lü (lu.html), Chen–Ueta (chen.html), Chen–Lee, Rikitake, Moore–Spiegel, Rayleigh–Bénard, Hadley, Dequan–Li, Coullet, Burke–Shaw, Sprott–Linz A–S, Finance, Bouali, Genesio–Tesi, Arnéodo, Newton–Leipnik, Rucklidge, Wang–Sun, Dadras, Halvorsen, Chua, Aizawa, Thomas, Rössler. Bulk centroid ≈ (−0.05, −0.02, 20.87) from warm 50k + 200k RK4 @ dt=0.001. RK4, not fourwing.html. Gold low-alpha trail, cap 650. RM = settled silhouette, no animate-on.