str(chemreac)
dotplot(temp ~ yield | time, chemreac, groups = cat,
strip = FALSE, strip.left = TRUE, type = c("p", "a"), layout = c(1,2),
auto.key = list(space = "right", title = "Catalyst", lines = TRUE))
summary(fm1 <- lm(yield ~ (time + temp + cat)^3, chemreac))
summary(fm2 <- lm(yield ~ time * temp + cat, chemreac))
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