Charles wrote:

> Is é fáth arná búaid a inchind dermait do búain
> a cind Chind Fáelad i cath Muige Rath acht in neoch
> ro·fácaib do degsaírse lebarda dia éis i nÉirinn.

Very good. I'd do a few things a little bit differently, though:

> 'neoch' is the dative singular of 'nech' but in the MI period it had
> become usual to use it as a relative pronoun introducing a statement
> in a partitive sense. 

Yes. It basically has the function of the "a + nasalisation + lenited relative clause" that I was talking about in the last 
installment. Note that what you have normalised, i.e. "in neoch", on the surface looks like a masculine, but it stands for 
what in OIr. would be expressed by a neuter. Actually we may even take the reading "i neoch" in the MS as a spelling 
for neuter "a neoch" - "i" and "a" are very frequently confused in Middle and Modern Irish MSS.

> 'ro·fácaib' is used because the action in the
> final clause was completed after the action in the main clause. 

This would be one of the functions of the ro-form of verbs in OIr. But be careful, with this text we are clearly in MidIr., 
and in that period ro-forms of the preterite (= perfects) had ousted the simple preterite in almost all places and 
functions. So the use of "ro" here doesn't necessarily imply the chronological precendence of one action over the 
other. You translated "ro·fácaib" as passive "(what) was left", but the form is actually 3rd sg. active "what he (= CF) 
left". Since "ro·fácaib" introduces a relative clause with object antecedent, a leniting relative construction is needed in 
MidIr: "ro·f*ácaib".

> cites 'saíre' as a form of 'saírse' + "craftsmanship" and offers a
> variant of E1 as an example.  

Yes. Final vowels have no independent value in MidIr., so there is no need to change "-saírsi" to "-saírse", we may just 
retain the former. (Apart from the fact that in OIr. it would be the correct ending.) Since "deg" + "saírsi" form a 
compound, we have lenition between the two: "degs*aírsi".

> It translates ' degsairi lebarda' as
> "well composed books". I kept 'lebarda' as a plural, but it seems to
> mean that 'lebor' is declined like a lenited dental.  

"leborda" is an adjective meaning "book..., pertaining to books", derived from "lebor" with the productive adjectival suffix 
"-dae". So the whole phrase literally means "a bookish good-craftmanship". We cannot say this in English, so we will 
have to rephrase it as "great mastership in books" or some other such phrase.

> Could the final 'r' be pronounced like an 'l'? 

No. Why should it?

We may also leave the spelling "Éirind" with final d.

So my version differs only slightly from Charles':

Is é fáth arná búaid a inchind dermait do búain a cind Chind F*aelad i cath Muigi Rath, a neoch ro·f*ácaib do degs*aírsi 
leabarda dia éis i nÉirind. 

"The reason why the beating of his brain of forgetfulness out of the head of Cenn Fáelad in the battle of Mag Rath is not 
a special, is that what he left behind himself in Ireland of great mastership in books."

Maybe the second part is not very good English syntax, but I hope it's intellegible.