This question is related to the
Answer
eval, print, showstat
Suppose one had 2 levels of evaluation and you only wanted to go back 1 level to uncover it's original components. That would be no problem if nothing was cleared, but very unfortunate if it did.
example,
a:=5*x^2-3*y^3:
b:=3*x^2+10*y^3:
c:=a+b
In this case, it is somewhat easy to see if the screen was erased to recover that c was equal to a+b indirectly.
It would actually be nice if we could call c and somehow get the underlying equation a+b
