Write sed commands to convert chapter$-$level headers

$$ from AsciiDoc to Markdown format $$ from Markdown to Org$-$Mode

$$ from Org$-$Mode to AsciiDoc

The input is taken from a file containing one link per line, no other text. Thus, if a file f contains the following links

$==$ Chapter header

$==$ Not a chapter header

$==$ Chapter with a $=$ in the middle $==$

$==$ Chapter with $=$s at the end $====$

## Chapter header

##

## Not a chapter header

## Chapter with a # in the middle ##

## Chapter with no #s at the end #####

$**$ Chapter header

$**$ Not a chapter header

$**$ Chapter with stars at the end $****$

$**$Not a chapter header

then the outputs should be

MYSTERY SEARCH$-$AND$-$REPLACE COMMAND AsciiDoc to Markdown$<$ f

header

$ sed $-$E $$MAGICAL ## Chapter header $==$ Not a chapter ## Chapter with a

$=$ in the middle ## Chapter with $=$s at the end $====$

## Chapter header ##

## Not a chapter header

## Chapter with a # in the middle ## ## Chapter with no #s at the end ##### $**$ Chapter header

$**$ Not a chapter header

$**$ Chapter with stars at the end $******$Not a chapter header

MYSTERY SEARCH$-$AND$-$REPLACE COMMAND Markdown to Org$-$Mode$<$ f

header

$ sed $-$E $$MAGICAL $==$ Chapter header $==$ Not a chapter $==$ Chapter with a

$=$ in the middle $====$ Chapter with $=$s at the end $====$

$**$ Chapter header $**$

## Not a chapter header

$**$ Chapter with a # in the middle

$**$ Chapter with no #s at the end

$**$ Chapter header

$**$ Not a chapter header

$**$ Chapter with stars at the end $******$Not a chapter header

MYSTERY SEARCH$-$AND$-$REPLACE COMMAND Org$-$Mode to AsciiDoc$<$ f

header

$ sed $-$E $$MAGICAL $==$ Chapter header $==$ Not a chapter $==$ Chapter with a

$=$ in the middle $====$ Chapter with $=$s at the end $====$

## Chapter header ##

## Not a chapter header

## Chapter with a # in the middle ## ## Chapter with no #s at the end ##### $==$ Chapter header

$**$ Not a chapter header

$==$ Chapter with stars at the end $******$Not a chapter header