Using the above knowledge, we went back to the program. We first assumed that the cryptotext character X coded a space and thus discarded these. We then replaced all the characters described above with one character.
It turned out that that character had relative frequency of about 10%. The second most frequent character amounted to about 9%.
Knowing this, we had an internal battle if we should first try Spanish or Italian as plaintext language. Eventually, we decided to give Italian a thorough attempt. The problem was that we knew no Italian. However, finding some samples of Italian on the WWW was no problem so we set out to solve it.
Using information about frequencies and common short words in Italian we used the interactive program to replace characters. After a while, we started feeling that we were actually seeing a real text form before our eyes.
We did not understand the text but using only the first two words as search string in AltaVista quite easily yields a hit for Dante Alighieri: The first five words produces a hit for Canto XXVI de L'Inferno. The codeword for this stage was placed after this text; it is EQUATOR.