Batch 240-A ACCEPTED -- attack on the section 8.6 engine: the (8.6.27) second slot's l-general window and coefficient shift (MMFLM86SlotWindowL, 11 declarations, no sorry)

The registered ledger is TWO holes (batch 239-A) and both are the section 8.6 engine (8.6.4)--(8.6.27)
in different currencies: the (8.4.25) cross contraction, which by batch 223-B IS the
window-synchronized (8.5.13) at the (8.5.4) states; and Theorem 8.8.9 source-faithful, whose l = 0 face
is that same (8.5.13)/display and whose l < 0 slice is the negative (Fock) face of the
(8.6.25)/(8.6.27) matching.  This batch attacks the second hole's l >= 1 slot at its generator slice.

New file Definitions/MMFLM86SlotWindowL.lean (namespace MM.FLM86SWL), all proved, all guarded, no
sorry/axiom/admit/native_decide, in FinalCheck:

* SUPPORT: canonWindowL form a b j l m c = Icc (<b,c>) (blockFirstIdx j l m <a,b> - <a,c>), with
  canonWindowL_zero = the landed MM.FLM86NPCA.canonWindow definitionally, mem_canonWindowL, and the
  support theorem blockOfShift_eq_zero_of_not_mem_canonWindowL (from the landed l-general vanishing
  lemmas MM.FLM86NPNA.blockOfShift_iotaVL_eq_zero_of_lt_left/right); consequently
  sum_eq_sum_canonWindowL_of_subset: any support containing the canonical window gives the same block
  sum, i.e. the canonical window is the MINIMAL support at iota(c);
* ARITHMETIC: blockFirstIdx_l_add (C_{l1+l2} = C_{l1} + l2), canonWindowL_add / canonWindowL_succ (the
  window grows by l), and the coefficient shift honestBlockCoeffJL_add_shift --
  coeff_{l1+l2}(Q) = coeff_{l1}(Q - l2) -- with its one-step form honestBlockCoeffJL_succ_shift and the
  reindexed p-form honestBlockCoeffJL_reindex: the coefficient at C_l - p - <a,c> is
  C(p + <a,c>, j + (-<a,b>).toNat), the form in which the generator face's a-index sum
  (flatGeneratorValueZ_eq_sum_binomCoeff) meets the slot.  The l-shift is the companion, in the shift
  index, of batch 233's MM.FLM86MBR.honestBlockCoeffJ_shift (the external index m).

NOT proved (recorded in the file header and NOTES section 140): the slot's identity itself at the
generator.  It needs the LHS evaluation for l >= 1 -- the field of the inserted state
YFam E a (-(j)-1) (creationExpVL b l (iotaVL b)) at iota(c) -- which for the slot's negative pairing is
the MODE-CROSSING engine (moving the b-side creation mode past the a-side field).  The same engine is
what the (8.4.25) cross contraction needs, so the two remaining holes have the same remaining content:
one engine, two currencies.  This is the consolidation this batch records.

Build: --- OK ---; footprint guards match (canonWindowL_zero/mem_canonWindowL/blockFirstIdx_l_add print
propext-only or the standard three; no sorryAx anywhere); forbidden_tokens: sorry=0; FinalCheck GREEN.
HANDOVER (row 4 and the module map), ROADMAP (#4 row) and NOTES (section 140) record the landing and the
remaining gap.
