The author asserts more than one proposition such that the
propositions cannot all be true. In such a case, the
propositions may be contradictories or they may be
- Montreal is about 200 km from Ottawa, while Toronto is
400 km from Ottawa. Toronto is closer to Ottawa than
- John is taller than Jake, and Jake is taller than Fred,
while Fred is taller than John.
Assume that one of the statements is true, and then use it as
a premise to show that one of the other statements is false.
26 May 1995