Sunday, October 17, 2004

Mutually Exclusive Thoughts

For some reason, students tend to think that certain things are mutually exclusive when they are not:

1. They think that "deterministic finite automata" and "nondeterministic finite automata" are disjoint sets, thus feel puzzled when someone says "a deterministic FA is also a nondeterministic FA". This is probably not their fault; the names really sound like they are opposites.

2. Then we have students who think that a strongly-connected graph is not a weakly-connected graph, even though the definition clearly shows that it is. OK, strong and weak are opposites...

3. Now we have students who think that there are 3 types of functions: injective, surjective, and bijective, and a function must belong to exactly one type. I dunno how they can get this impression.

I am waiting some students to say "a tree is not a graph", or something like that.

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