... but as I was saying, you should be careful with using the de as you've defined it. It's really easy to run into weird problems when you need to copy/paste code. It's trivial here, but when you have more complicated expressions that you have to deal with, finding this problem could take a while. So having a "guarantee" that variable names copy/paste properly is quite important.
In the example below the problem goes away (at least here) if one defines:
de:=`δx`; #no space
here is the raw code:
a:=de * 3;
#copy paste the delta x from the 2d math from Eq above , into the next expression to to define b:
b:= Î´x * 3 ;
#again copy paste the two - note now there is an extra space
#in one of them, between the quotes! - the delta we've defined
#is not the same as what got copied!