KMK final-size: F=R_∞−1+exp(−R_0·R_∞)=0; dF/dR_∞|_0=1−R_0; outbreak iff R_0>1

Sympy-exact symbolic witness of the Kermack-McKendrick final-size equation implicit canonical form and the outbreak-threshold linearisation. Setup: R_∞ (Rinf), R_0 — both positive symbols. Implicit final-size equation: F(R_∞; R_0) = R_∞…