# note: Only 4 code-length codes declared, the minimum the 4-bit field
#   allows.
# expect: ok
# exercises: Restricts the code-length alphabet to {17, 18, 0, 1}, so
#   lengths can only be 0 or 1 plus the two zero-run escapes.
lossless
code dist lengths 1 1
code dist codelen 1 1 18x38
code dist num_codes 4