Editing Bra–ket notation (section)

===Reuse of symbols===
It is common to use the same symbol for ''labels'' and ''constants''. For example, <math>\hat \alpha |\alpha\rangle = \alpha |\alpha \rangle</math>, where the symbol <math>\alpha</math> is used simultaneously as the ''name of the operator'' <math>\hat \alpha</math>, its ''eigenvector'' <math>|\alpha\rangle</math> and the associated ''eigenvalue'' <math>\alpha</math>. Sometimes the ''hat'' is also dropped for operators, and one can see notation such as <math>A |a\rangle = a |a \rangle</math>.<ref>{{harvnb|Sakurai|Napolitano|2021}} Sec 1.2, 1.3</ref>