Statement

An alien race decided to create a new alphabet (alienabc) based on the English alphabet. For each letter in the English alphabet, they can: (1) [\bullet] Exclude the letter entirely. (2) [\bullet] Include the letter (e.g., a \to a). (3) [\bullet] Include the letter in a doubled form (e.g., a \to aa) (aa is one letter in their new alphabet). (4) [\bullet] Include both the single and double versions of the letter (e.g., a \to a aa). They wrote down the alienabc, each alien letter exactly once, in their own, alien alphabetic order. The order of letters might differ from the English alphabetic order, and a letter and its doubled version (e.g., a and aa) do not have to be adjacent in the alienabc. Unfortunately, they did this without any separator. Can you reconstruct the alienabc? You only have to insert spaces between the alien 'letters'. For example, if they wrote adccb, then the alienabc is clearly a d cc b...