Is it valid to assign a slice of an array or vector to an overlapping slice of the same object? R seems to do the right thing but I can't find anything where it promises to. > a <- 1:12 > a[4:12] <- a[1:9] > a [1] 1 2 3 1 2 3 4 5 6 7 8 9 > b <- 1:12 > b[1:9] <- b[4:12] > b [1] 4 5 6 7 8 9 10 11 12 10 11 12