Hi guys,

Firstly, thank you so much for the open textbooks. I'm using the Precalculus one as suggested by Coursera. I'm enjoying it so far, but I do have a question regarding the aforementioned exercise.

The book states (bottom of p.14):

"In Exercises 8 - 19, write the set using interval notation."

The particular set in question is as follows: { x | x != -3, 4 }

The answer is given as: (-infinity, -3) U (-3, 4) U (4, infinity)

I understand why the answer is what it is, but I wonder if the actual set definition should be: { x | x != 3, x != 4 }. Having looked around at other examples online (e.g.

http://www.mathsisfun.com/sets/set-builder-notation.html - scroll all the way to the bottom), each condition seems to be listed explicitly. I misunderstood the comma here, and thought the set was all x such that x is not equal to -3, and 4 is an element of the set.

Is it typical to condense conditions using commas like this, or is this a minor correction that should be made?

Kind regards,

John