What does the 'coef' argument to topTable() actually do?
I know it says in the manual:

column number or column name specifying which coefficient or
contrast of the linear model is of interest

But what does that mean mathematically?  Why does specifying
the coefficient alter the results of the top table?  Either a probe
is differentially expressed or it isn't, right?

I'm having trouble conceptualizing why there are multiple coefficients
at this stage at all.  Suppose my contrast is "MUvsWT=MU-WT".
How do you get more than one result when you subtract WT from MU?

If I run topTable(fit,coef=1) does that get me MU, WT, or MU-WT?
If I run topTable(fit, coef=2) does that get me MU, WT, or MU-WT?
If I run topTable(fit, coef=0) or topTable(fit, coef=2), I get an error.
Which of those isn't a coefficient and why not?

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