MathML generated by MathToWeb
A MathML example displaying the extensible AMS Latex arrows:   \xleftarrow  and  \xrightarrow.

$A{\displaystyle \stackrel{ \alpha \pm 2-1 }{⟵}}B{\displaystyle \underset{ H^{+} }{\overset{ {130}^{\circ }C }{⟶}}}C$ $A \; \xleftarrow{\alpha \pm 2 - 1} \; B \; \xrightarrow[H^+]{{130}^\circ C} \; C$

<math xmlns="http://www.w3.org/1998/Math/MathML">
<mrow>
	<mi>A</mi>
	<mspace width="0.278 em" />
	<mstyle displaystyle="true">
		<mover>
			<mo stretchy="true">&xlarr;</mo>
			<mrow>
				<mo>&nbsp;</mo>
				<mi>&alpha;</mi>
				<mo>&plusmn;</mo>
				<mn>2</mn>
				<mo>-</mo>
				<mn>1</mn>
				<mo>&nbsp;</mo>
			</mrow>
		</mover>
	</mstyle>
	<mspace width="0.278 em" />
	<mi>B</mi>
	<mspace width="0.278 em" />
	<mstyle displaystyle="true">
		<munderover>
			<mo stretchy="true">&xrarr;</mo>
			<mrow>
				<mo>&nbsp;</mo>
				<msup>
					<mi>H</mi>
					<mo>+</mo>
				</msup>
				<mo>&nbsp;</mo>
			</mrow>
			<mrow>
				<mo>&nbsp;</mo>
				<msup>
					<mn>130</mn>
					<mo>&compfn;</mo>
				</msup>
				<mi>C</mi>
				<mo>&nbsp;</mo>
			</mrow>
		</munderover>
	</mstyle>
	<mspace width="0.278 em" />
	<mi>C</mi>
</mrow>
</math>