This is a mockup of a tool with the ambitious intention of becoming the standard format for derivations.
The tool aims to do several things:
Divide both sides by $(a-b)$
[only valid if $a-b \ne 0$, i.e. $a \ne b$]
$$a+b = b$$
Substitution $(a=b)$
$$2b = b$$
Divide both sides by $b$
[only valid if $b \ne 0$]
$$2 = 1$$