Example ex5-09
(a + b)
a b
⁢
(c + d)
c d
a b
c d
<math>
<semantics>
<mrow>
<semantics>
<mrow><mo>(</mo><mi>a</mi> <mo>+</mo> <mi>b</mi><mo>)</mo></mrow>
<annotation-xml encoding="MathML-Content">
<apply><plus/><ci>a</ci> <ci>b</ci></apply>
</annotation-xml>
</semantics>
<mo>⁢</mo>
<semantics>
<mrow><mo>(</mo><mi>c</mi> <mo>+</mo> <mi>d</mi><mo>)</mo></mrow>
<annotation-xml encoding="MathML-Content">
<apply><plus/><ci>c</ci> <ci>d</ci></apply>
</annotation-xml>
</semantics>
</mrow>
<annotation-xml encoding="MathML-Content">
<apply><times/>
<apply><plus/><ci>a</ci> <ci>b</ci></apply>
<apply><plus/><ci>c</ci> <ci>d</ci></apply>
</apply>
</annotation-xml>
</semantics>
</math>