I'm writing an app that does something like a custom number (licence) place generator tool where if I ask for the plate "robin" it will suggest I try: r0bin rob1n r0b1n Are there any published algorithms which can do this? It has to be able to handle replacing single letters with multiples, e.g. m with rn and vise-versa and not fall over if it replaces an i with an l then comes to check the l and replaces it back to an i. The list of what gets swapped with what is going to be user input but I'm not expecting a huge list, possibly 10 pairs at most. I'll be implementing this in Ruby or Python but I should be able to convert code from any other language.