The scratch area also shows a list of constraints, this is a set of definitional equalities which must hold for the scratch area to represent well formed partial expressions. Constraints are being added or deleted as an object is being edited.
It is possible to select a constraint and solve it by choosing ``solve'' with the right button. This will take a constraint of the form
where e does not contain placeholders and replace all occurrences of 
with 
in
the scratch area.