R help - Dec 2008 - Tukey on interaction means after lmer

Dear Colleagues,
I fit this model:

mod1 <- lmer(x~category*comp+(1|id),data=impchiefsrm)

where category has 4 levels and comp has 8 levels.

These work:

glht(mod1, linfct=mcp(category="Tukey")
glht(mod1, linfct=mcp(comp="Tukey")

What I'd like is (conceptually):

glht(mod1, linfct=mcp(category:comp="Tukey")

but it gives a syntax error.

Any help is appreciated.

Thanks,

Larry

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