Design a regular expression to search for files, in a folder. The file names that you search for should satisfy AT LEAST ONE of the following conditions: 1. Contains Grade" as a substring but does not contain the letter 'F' or 'f'. 2. Contains the letters 'u','c','s','b'. 3. Is named "theory. The file names contain only English letters (small and capital) and numbers 0 to 9. That is, the alphabet associated with the file names is = {a,...,2,A,...,2,0,...,9}. In particular, the file names do not contain spaces or special characters