```
make.names(c("a and b", "a-and-b"), unique = TRUE)
# "a.and.b" "a.and.b.1"
make.names(c("a and b", "a_and_b"), unique = TRUE)
# "a.and.b" "a_and_b"
make.names(c("a and b", "a_and_b"), unique = TRUE, allow_ = FALSE)
# "a.and.b" "a.and.b.1"
make.names(c("", "X"), unique = TRUE)
# "X.1" "X" currently; R up to 3.0.2 gave "X" "X.1"
state.name[make.names(state.name) != state.name] # those 10 with a space
```

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