— procedure: bit-string-append bit-string-1 bit-string-2

Appends the two bit string arguments, returning a newly allocated bit string as its result. In the result, the bits copied from bit-string-1 are less significant (smaller indices) than those copied from bit-string-2.

— procedure: bit-substring bit-string start end

Returns a newly allocated bit string whose bits are copied from bit-string, starting at index start (inclusive) and ending at end (exclusive).