Nothing

```
# Return the part of labels(terms(formula.full)) that is not included in formula.reduced
# Doesn't care if formula.reduced contains something not in formula.full
labels_interesting <- function(formula.full, formula.reduced) {
mf <- attr(terms(formula.full), "factors")
mr <- attr(terms(formula.reduced), "factors")
labs <- character()
if(attr(terms(formula.full), "intercept") > attr(terms(formula.reduced), "intercept"))
labs <- c("(Intercept)", labs)
if(length(mf) > 0) {
varorder <- match(row.names(mr), row.names(mf))
newvars <- setdiff(1:nrow(mf), varorder)
# What do terms >= 2 mean?
interesting <- sapply(1:ncol(mf), function(i) {
term <- mf[,i,drop=FALSE]
if(any(term[newvars] != 0)) return(TRUE)
term <- term[varorder]
term[is.na(term)] <- 0 # Variables only in formula.reduced
for(j in 1:ncol(mr)) {
if(all((term!=0) == (mr[,j]!=0))) return(FALSE)
}
return(TRUE)
})
labs <- c(labs, labels(terms(formula.full))[interesting])
}
labs
}
# Check that formula.reduced is nested within formula.full and that formula.full includes something extra.
check_isnested <- function(formula.full, formula.reduced) {
# Check that the reduced model is nested within the full model
if(length(labels_interesting(formula.reduced, formula.full))>0) stop("The reduced model includes something not in the full model.")
# Check that the full model includes something in addition to the reduced model
if(length(labels_interesting(formula.full, formula.reduced)) == 0) stop("The full model is equal to the reduced model.")
}
```

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