MathML3 specification example (modified)
<math xmlns="http://www.w3.org/1998/Math/MathML"> <apply> <ci>f</ci> <apply id="share-t1"> <ci>f</ci> <apply id="share-t11"> <ci>f</ci> <ci>a</ci> <ci>a</ci> </apply> <share href="#share-t11"/> </apply> <share href="#share-t1"/> </apply> </math>