"Two and only"

I wrote on the marginalia to Chapman (p. 91) caring to transcribe yet again the decalogue for us. For Chapman numbers them

1. Make your contribution as informative as is required
2. Not _more_ informative

1. Be truthful
2. Be serious

1. Be relevant ("two and only")

1. Avoid obscurity -- Chapman misquotes this as 'ambiguity'
2. Avoid ambiguity
3. Be brief -- avoid unnecessary prolixity (sic). Chapman omits this.
4. Be orderly

which do sum up

2
+
2
+
1
+
4
= 9

and adding the extra maxim on WoW xvii we do get the 'dekalogos'. Q. E. D.

It strikes me as funny that Chapman numbers 'be relevant' as the "one" and only.