title: Numbering each line of equation in Latex
body: <p>Is there a way to label every line of multiline equation with a separate subindex?</p>
  
  <p>For example, I would like to obtain sth like (in the output)</p>
  
  <p>a = b (1.23.1)</p>
  
  <p>c = d (1.23.2)</p>
  
  <p>= f (1.23.3)</p>
  
  <p>and then be able to refer to either whole multiline equation ("As seen in 1.23 bla bla bla...") or to a specific line ("In 1.23.3 we have redefined d...").</p>