concept
R19 bistable switch
ṡ = g·s − s³ + hThe universal cubic substrate: bistable detection, and at criticality (g=0) cube-root amplification.
The R19 switch is the one cubic the whole volume is built on. The state s obeys ṡ = g·s − s³ + h: with g>0 it is bistable (an all-or-none detector), and at the critical point g=0 the same equation compresses as the cube root s = h^(1/3).
Its discontinuous threshold is the spinodal 2·(g/3)^1.5, which sets the emergence order of the master genes and the finite bistable drive window 2·spinodal(g). The same cubic appears as the tip-link switch (§1), the cochlear amplifier (§2), and the four deafness loci (§3).