code: public LcpMonotoneMinimalPerfectHashFunction<T> build() throws IOException {
  			if (built) throw new IllegalStateException("This builder has been already used");
  			built = true;
  			return new LcpMonotoneMinimalPerfectHashFunction<>(keys, numKeys, transform, signatureWidth, tempDir);
  		}
docs: Builds an LCP monotone minimal perfect hash function.
  
  @return an {@link LcpMonotoneMinimalPerfectHashFunction} instance with the specified parameters.
  @throws IllegalStateException if called more than once.