question about constructing hypothesis test

[shuaichenli]

Dear Prof. Wu,

Although the user's guide of DSS is informative, I have two questions about constructing a hypothesis test in DMLtest.multiFactor function.
In '3.4.1 Hypothesis testing in general experimental design', you give an example to explain how to test the effect of Strain B verse Strain A (coef = 2). I think the effect of C vs A can also be tested using coef = 3.
However, how can I construct coef or contrast to test the effect of B vs C ?
If I cannot test it in this design, can I just reorder the level of Strain to test B vs C, like changing levels =c("A", "B", "C") to levels = c("B", "A", "C"), and then fit new design again to test B vs C ? It works in my data, but is it a right and simple way ?

Besides, in the last paragraph of 3.4.1, you set contrast as (0, 1, -1, 0) to test B = C. Do I understand correctly that it can also be set as (0, -1, 1, 0) ?

Thanks a lot.
Shuaichen Li