SP-Ps1 app for iPhone and iPad

SP – PS1 is a software tool made for teachers and students. Its goal is to provide a better comprehension about strings and language operations. You can edit and save language expressions to see the results of certain operations.
String operations are length (|s|) and concatenation. Language operations are union (U), concatenation, exponentiation (^n), kleene closure (*), positive closure (+) and one or zero (?).
If you want to know more about this tool, you can download the SP-Ps1 tutorial for free from the iBooks Store. The book is named “What is SP-Ps1”.