A length n vector of a's, appended to by a length m vector of a's, results in a length (n + m) vector of a's. This is a safety guarantee that is statically chec

A length n vector of a's, appended to by a length m vector of a's, results in a length (n + m) vector of a's. This is a safety guarantee that is statically checked at compile time rather than dynamically checked at run time.