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Next: Exercise Chapter 2.7 Up: Solutions and Comments Previous: Exercise Chapter 2.5

Exercise Chapter 2.6

  1. b:- a.

    Note that b is true if a is true.

  2. c:- a.
    c:- b.

    Here we have a straight use of disjunction.

  3. c:- a, b.

    Here is a straightforward example of a conjunction.

  4. d:- a, b.
    d:- a, c.

    This is a hard one. We cannot (yet) write what we want to write: that is, d:- a, (b or c). Here, we can use de Morgan's law: this is the equivalence: a (b c) d (a b) (a c) d.

  5. b:- a.

    This is hard too. The obvious solution is:

    not a.

    but this is not allowed. Consequently, we have to transform the expression using the logical equivalence a b b a.

Paul Brna
Mon May 24 20:14:48 BST 1999