A Demazure atom 
is a polynomial indexed by a weak composition 
, defined by the recursion for key
polynomials with every isobaric divided difference operator 
replaced by 
. The initial value is 
for weakly decreasing
(Mason 2009). The atoms form a basis
that refines the key-polynomial basis.
The Demazure 
-atoms
use instead 
, so 
and 
. In the expansion 
,
Alexandersson (2026) found a coefficient with sole negative term 
for 
and 
. Degree 14 is minimal only within the
tested family of length-
, size-
compositions with entries 0, 1, and 2. The example yields
failures of flagged LLT polynomial atom positivity
and of the corresponding stable-atom positivity assertion for modified nonsymmetric
Macdonald polynomials. It does not refute
symmetric Macdonald positivity.
