1. drop(0, L) = L

    Example: drop(0, [2,4,6]) = [2,4,6].

  2. drop(n, [ ]) = [ ]

    Example: drop(5, [ ]) = [ ].

  3. drop(n, L) = drop(n-1, tail(L))

    Example: drop(3, [2,4,6,8,10]) = drop(2, [4,6,8,10]) = [8,10].