for ra, rb being Real
for g being continuous Function of (Closed-Interval-TSpace (ra,rb)),R^1
for s1, s2 being Real st ra < rb & s1 * s2 < 0 & s1 = g . ra & s2 = g . rb holds
ex r1 being Real st
( g . r1 = 0 & ra < r1 & r1 < rb )