 Order preservation for scalar entropy solutions

Subtract the weak equation for $u-v$ from its Kato inequality for scalar conservation laws and divide by two. The result is an inequality for $(v-u{)}_{+}$ with a flux bounded in magnitude by $M(v-u{)}_{+}$. The same shrinking-interval argument proves $u_0\ge v_0\Rightarrow u\ge v$ almost everywhere. Choosing the constant solution $v=0$ proves preservation of nonnegativity even when $f(0)\ne 0$. Two-sided absolute-value contraction alone should not be mistaken for this one-sided comparison proof.