Consider the "letter game" patterned after an article by Don Gernes from Ponderosa High School.We have three undefined terms, the lettersM,I, andU, and one definition, "xmeans any string ofI's andU's." Finally, there are four postulates for this letter game.

Postulates

1. If a string of letters ends inI, you may add aUat the end. This is theaddition rule.

2. If you haveMx, then you may addxto getMxxby what we call thedoubling rule.

3. If threeI's occurthat is,IIIthen you may replace that string byU. We call this thesubstitution rule.

4. IfUUoccurs, you drop it. This is thedeletion rule.

MIIUIIU - SELECT WHICH RULE?