Rein Prank* (Estonia), prank@cs.ut.ee
A Scheme for Conservative Use of Computer Algebra

In Tartu University we are using a Propositional Formula Manipulation Assistant
where the instructor can fix Subformula Location Mode:
a) LINEAR (shifting the ends of highlighted substring),
b) TREE (usual mode of CA programs)
and Subformula Replacing Mode:
a) IMMEDIATE (input of replacing string),
b) RULE (the student chooses the rule/procedure from menu),
c) INPUTRULE (the student enters the rewrite rule).
Such scheme does not change the traditional role of the student and allows to
implement many tutoring strategies. We discuss the problems of didactic
adequacy of the interface.