Commas and vowel pairs

[Richard Curnow <richard@rrbcurnow.freeuk.com>]

In chapter 3 of the Ref. Grammar, there is a statement 

"Commas are never required: no two Lojban words differ solely because
of the presence or placement of a comma."

There are examples of type 3 fu'ivla in chapter 4 such as 

bangrkore,a

where the comma is required to separate an invalid vowel pair. The
chapter 3 statement implies the comma can be removed without change of
meaning or validity. This implies any of the 25 vowel pairs of the form
[aeiou][aeiou] could occur in a cmene or fu'ivla, not just 

ai au ei oi i[aeiou] u[aeiou]

+ iy uy (cmene only)

as implied by other parts of chapter 4. What degree of validity
checking is required on adjacent vowels that aren't separated by commas
or apostrophes? Hence what are the valid vowel arrangements in cmene
and fu'ivla? (It's pretty clear that only ai,au,ei,oi are valid in
gismu and lujvo, by the way they are constructed.)

-- 
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Richard P. Curnow rpc@myself.com
Weston-super-Mare
United Kingdom http://go.to/richard.curnow/