I don't want more differences, just difference in a different place. You could have, for example, defined Arc'' as identical to Arc except gzip-compressed. On

I don't want more differences, just difference in a different place. You could have, for example, defined Arc'' as identical to Arc except gzip-compressed. Once you have a parse tree, Arc, Arc' and Arc'' are identical, but Arc'' is actually more concise. But that's useless, because nobody is saying conciseness and power are identical. Arc' is no more likely to educate anybody than Arc'' is.