[error] /home/alex/Desktop/lfa/lfa-etapa2/skel-scala/src/main/scala/Regex.scala:8:59: type mismatch;
[error]  found   : Unit
[error]  required: List[Either[Char,Char]]
[error]   def preprocess(s:List[Char]): List[Either[Char,Char]] = {}
[error]                                                           ^
[error] /home/alex/Desktop/lfa/lfa-etapa2/skel-scala/src/main/scala/Regex.scala:11:39: type mismatch;
[error]  found   : Unit
[error]  required: String
[error]   def toPrenex(str: String): String = {}
[error]                                       ^
[error] two errors found
