This is a test file with some referenced equations, line $$ this $$

Some equations might be inside of text, $$ for example $$ this one.

Some equations might be on start of paragraphs:

$$ start $$ of paragraph.

Other might be on separate paragraphs of their own:

$$ separate $$

Some of those can be labelled:

This is a test file with some referenced equations, line

  ---------------------------------------------------------------- ------
                             $$ this $$                            $$(1)$
                                                                        $
  ---------------------------------------------------------------- ------

Some equations might be inside of text,

  ---------------------------------------------------------------- ------
                         $$ for example $$                         $$(2)$
                                                                        $
  ---------------------------------------------------------------- ------

this one.

Some equations might be on start of paragraphs:

  ---------------------------------------------------------------- ------
                            $$ start $$                            $$(3)$
                                                                        $
  ---------------------------------------------------------------- ------

of paragraph.

Other might be on separate paragraphs of their own:

  ---------------------------------------------------------------- ------
                           $$ separate $$                          $$(4)$
                                                                        $
  ---------------------------------------------------------------- ------

Then they can be referenced:

Individually eq. 1, eq. 2, eq. 3, eq. 4

Or in groups eqns. 1, 2, 4

Groups will be compacted eqns. 1-4