Abstract
This paper investigates indicators of formal thinking in geometry problems. A sample of 20
tertiary students were given a test item which restricted the information that was available to
them for use in the proof The test item was administered before and after a course on the
development of non-Euclidean geometry. Before the course, the students were not able to deal
adequately with restrictions to the knowledge they could assume. After the course, students
appeared to cope well with the notion of restrictions to assumed knowledge, but this
accommodation did not translate into the writing of acceptable proofs. The conclusions drawn
are: (i) writing proofs where there are restrictions to assumed knowledge clearly involves a
sophisticated form of deductive reasoning; and, (ii) an indicator of advanced formal thinking is
the ability to develop a proof H!here cases, which take into account different relationships (as
opposed to properties) between necessary and sufficient conditions, are accommodated.
Paul White & John Pegg
A DESCRIPTION OF STUDENT RESPONSES TO RESTRICTIONS ON ASSUMED KNOWLEDGE