Entry 740 derives a valid local fact from each double residue
C=(CKCE0CB).
At all certified corners,
CK=CB=0,
so the grade-zero extension operator
L0(C)(X)=XCK−CBX
vanishes. The exported principal columns vec(CE) are
therefore unobstructed by this local corner operator. In particular, the
horizontal line
λ=x12−x13+x23
passes the first available corner-indicial gate.
What this proves
The exact conclusion is
L0(C)vec(CE)=0at every resolved corner.
This is stable under the quadratic involutions and the even
μ2-trace. It rules out the simplest local killing mechanism and is
genuine progress beyond the horizontal rank computation.
The version-two packet adds the zero matrix for L0(C), but still does
not export:
the vertex differential ∂Vq;
the preceding edge differential ∂Eq−1;
the following edge differential ∂Eq as part of a cochain
complex;
the degreewise restriction on ker∂Vq;
the chain identities ∂2=0 and
∂Eδ=δ∂V.
Moreover, L0(C) is initially an indicial extension operator. Calling
it an internal cochain differential requires the adjacent graded terms and
the square-zero comparison; the zero matrix alone makes that comparison
vacuous at only one spot.
Thus the statement in Entry 740 that the principal columns are not internal
boundaries is valid only relative to the displayed zero L0 image. It
does not yet exclude