V.T202 — tau Interpolation Function

tau Interpolation Function: mu_tau(x) = x/sqrt(1+x^2), DERIVED from capacity gradient profile. Deep MOND (x<<1): mu->x, g_obs=sqrt(g_bar*a_0) (BTFR). Newtonian (x>>1): mu->1, g_obs=g_bar. Same as 'standard' MOND interpolation, here derived not assumed.