Platt theorem: P0, P_max, slope, I_k, Taylor — 5 P-I canonical anchors

Sympy-exact symbolic witness of the Platt P-I saturation canonical identities. Setup: P_B_m, B, α, I_0, I — all positive symbols. Surface production at z=0: P_0 = B·P_B_m·(1 − e^(−α·I_0/P_B_m)) (sympy canonical 'B*P_B_m -…