REVIEW 3 major objections 5 minor 20 references
Characterizing $3$-dimensional manifolds represented as connected sums of Lens spaces, $S^2 \times S^1$, and torus bundles over the circle by certain Morse-Bott functions
T0 review · 3 major / 5 minor · reviewed 2026-08-11 · deepseek-v4-flash
Pith's one-line read A closed, connected, orientable 3-manifold has a Morse-Bott function whose regular preimages are spheres and tori and whose singular set is made of points, circles, spheres, tori, and projective planes exactly when it is a connected sum…
desk verdict A genuine extension of Saeki's theorem with a solid converse, but the only-if proof of Theorem 2 has a load-bearing gap in STEP 1-2 that needs to be filled before the paper is complete. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The Reeb digraph of $f$, the quotient space whose points are connected components of preimages of points of $\mathbb{R}$, with vertices at components containing singular points, edges oriented by the value of $f$, and edges colored according to whether a generic preimage is $S^2$ or $S^1 \times S^1$. The proof deforms the function locally, using singularity theory, until the torus-fibered edges form disjoint closed arcs $I$ and circles $C$; the preimage of a neighborhood of $I$ is a punctured lens space, $S^2 \times S^1$, or $S^3$, while the preimage of a neighborhood of $C$ is a punctured torus bundle. The resulting Reeb digraph can be taken to be a cactus graph, and this structure is the basis of Theorem 3, which realizes prescribed labeled digraphs with torus-fibered cycles.
What would settle it
To test the central claim, take a closed connected orientable 3-manifold whose prime decomposition has a factor that is neither a lens space, $S^2 \times S^1$, nor a torus bundle over $S^1$ (for instance a hyperbolic 3-manifold) and search for a Morse-Bott function satisfying conditions (1)-(3); finding one would refute the theorem. A more direct check of the proof's crux is to compute, in the model Reeb digraph with a single torus-fibered circle, the preimage of a small regular neighborhood of that circle and verify it is a punctured torus bundle, since a failure would show the STEP 1-2 assertion false.
Extended reading notes
Core claim
The central claim is Theorem 2: the three conditions on $f$ are equivalent to $M$ being diffeomorphic to $S^3$, $S^1 \times S^2$, a lens space, a torus bundle over $S^1$, or a connected sum of these manifolds. In the only-if direction, the proof analyzes the Reeb digraph of $f$ near each type of singular set and asserts that the torus-fibered edges organize into closed arcs and circles; the preimage of a small neighborhood of an arc is a punctured lens space, a punctured $S^2 \times S^1$, or a punctured $S^3$, and the preimage of a small neighborhood of a circle is a punctured torus bundle. These pieces glue along their $S^2$ boundary spheres, presenting $M$ as the required connected sum. In the converse direction, each building block is given an explicit Morse-Bott function, and these functions are glued along spheres to cover arbitrary connected sums.
Load-bearing premise
The only-if direction assumes, without a detailed proof, that after local homotopies the torus-fibered edges of the Reeb digraph form closed arcs and circles whose small-neighborhood preimages are punctured lens spaces, punctured $S^2 \times S^1$, or punctured $S^3$, and punctured torus bundles, respectively; if this structural assertion fails, the connected-sum decomposition of $M$ is not established.
Editorial extensions
If this is right
- Every manifold in the characterized class admits an explicit Morse-Bott function of the stated type, and its Reeb digraph can be chosen to be a cactus graph.
- The class of manifolds carrying such functions is closed under connected sums, since the functions glue along $S^2$ boundaries and the construction is local.
- Torus bundles over $S^1$, which are not connected sums of lens spaces and copies of $S^2 \times S^1$, now lie inside the same function-theoretic characterization.
- The paper gives an affirmative answer to Problem 1 in the stated regime: a labeled digraph with prescribed torus-fibered cycles is realized by such a Morse-Bott function on a suitable connected sum.
Reading between the lines
- The unproved 'We can also check' assertions in STEP 1-2 are the structural crux of the only-if direction; if a detailed proof can be supplied, the connected-sum decomposition follows, and if one of them fails, the converse is not established as written.
- A natural testable extension is to non-orientable 3-manifolds, where the allowed singular set may need additional types such as the Klein bottle and the classification may involve different summands.
- The cactus Reeb digraph suggests a combinatorial calculus for these functions: local moves that create or cancel torus-fibered cycles may correspond to surgeries between connected-summands, which could simplify the functions.
- One could try to detect torus-bundle summands directly from the function data by counting torus-fibered cycles in the Reeb digraph, though the paper does not establish such a numerical invariant.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper characterizes closed connected orientable 3-manifolds that admit a Morse-Bott function whose regular preimages are disjoint unions of S^2 and S^1 x S^1, whose singular set is a disjoint union of points, circles, tori/spheres, and RP^2, and whose non-extremal singularities are Morse. Theorem 2 states that this class is exactly the class of connected sums of copies of S^3, S^1 x S^2, lens spaces, and torus bundles over S^1. The proof has two parts: STEP 1 attempts to show that any such function forces the domain to lie in this class, via local analysis of Reeb graph vertices and local deformations that simplify the 'red' (torus-fibered) edges; STEP 2 constructs such functions on each allowed summand and glues them. The paper also states Theorem 3 as a graph-theoretic realization result in the spirit of [11, Problem 1].
Significance. If Theorem 2 is correct, it gives a natural Morse-Bott analogue of Saeki's classification [18] and answers a problem posed in the author's preprint [11]. The converse construction is concrete and the statement is well motivated. However, the only-if direction depends on an unproved structural lemma about the Reeb digraph after local deformation, and this lemma is precisely what connects torus-fibered edges to torus-bundle summands. The paper also relies on the author's own preprint [11] for the central local moves, despite claiming to be essentially self-contained. The result is potentially valuable, but the manuscript as written does not fully establish the only-if direction.
major comments (3)
- The only-if direction hinges on the assertion, introduced by 'We can also check', that after iterating the Figure 2 local changes the red-edge complex consists of arcs I and circles C with q_{f0}^{-1}(N(I)) diffeomorphic to a lens space, S^2 x S^1, or S^3 with two open D^3 removed, and q_{f0}^{-1}(N(C)) diffeomorphic to a torus bundle over S^1 with finitely many open D^3 removed. No proof of this assertion is given. It is not a routine consequence of the preceding local cases: CASE 1-1-3 includes a local extremum whose singular set is S^1 x S^1 and whose neighborhood preimage is S^1 x S^1 x D^1, whose boundary has two torus components. If a red arc or circle passes through such a vertex, the boundary of the total preimage of a small neighborhood need not be spherical, contradicting the claimed D^3-removal description. The text does not show that the Figure 2 moves eliminate all such configurations, nor does it specify how N(I) or N(C) is chosen to avoid torus boundary components. This gap is load-bearing: without this structural lemma, the only-if direction of Theorem 2 does not establish the decomposition into lens spaces and torus bundles.
- The simplification mechanism itself is not independently established in this manuscript. The local changes in Figure 2 are described only by a figure and a reference to the author's preprint [11]; the text states that each change is realized by a small homotopy and uses a fact about a local preimage being S^1 x D^2 with two D^3's removed, but it does not give the homotopies, does not verify that the moves preserve hypotheses (1)-(3), and does not prove that a suitable iteration terminates at the claimed normal form. Because the paper advertises itself as essentially self-contained, this delegation to an unpublished preprint is a serious gap that should be closed by proving the required statements or by quoting them with full details.
- Even if the structural lemma were accepted, the step from the asserted preimage descriptions to the conclusion that M is obtained by removing D^3's from a finite family of torus bundles, lens spaces, S^2 x S^1, and S^3 and gluing along S^2 boundaries is not fully justified. The proof does not explain how the decomposition of the Reeb digraph into arcs I and circles C is derived from the original f, nor does it verify that every component of M is covered exactly once by the neighborhoods N(I), N(C), and the vertex neighborhoods from STEP 1-1, nor that the gluing maps identify entire spherical boundary components. A precise statement and proof of this decomposition would resolve the gap.
minor comments (5)
- There are several typographical errors, e.g., 'Lens sp aces', 'res ult', 'connected sums of connected sums', and 'self-contained way essentially'; these should be corrected.
- The figures carry a large part of the proof, but the local moves in Figure 2 and the Reeb digraphs in Figures 3 and 4 are not described combinatorially in the text. Please add explicit descriptions so that the reader can verify the normal-form claim and the reconstruction without consulting [11] or relying on visual inspection.
- The gluing construction in STEP 2 should state how the local Morse-Bott functions are smoothed across the S^2 gluing spheres while keeping the singular set of the required type and keeping the non-extremal singularities Morse.
- The notation in the proof of Theorem 3, including K0', C0,j, ev_C,K',l, and ev_C,l/h, is introduced quickly and is hard to follow; a formal definition or a figure would improve readability, and the dependence on [10,11] for essential local constructions should be stated precisely.
- The claim that torus bundles over the circle are not diffeomorphic to connected sums of lens spaces and copies of S^1 x S^2 is used implicitly to distinguish summands; it should be justified by a short argument, for example using fundamental groups.
Circularity Check
Theorem 2 is not a formal restatement of its hypotheses and retains independent content anchored by Saeki's theorem, but load-bearing local moves are imported from the author's own preprint [11], Theorem 3 delegates constructions to [8,9,10,11], and the STEP 1-2 'We can also check' preimage classifications are an unproved pivotal gap, so the claim of essential self-containment is substantially…
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self citation load bearing
[Section 3, STEP 1-2, paragraph introducing FIGURE 2]
"We also present additional arguments and figures from [11]. FIGURE 1 shows local forms of simple STF Morse functions by Reeb digraphs with information on preimages. ... FIGURE 2 shows local changes. Each homotopy is realized by a suitable small homotopy. This is from fundamental singularity theory together with the fundamental fact on the 3-dimensional manifold theory: the preimage of the presented local graph (local complex) is diffeomorphic to a manifold obtained by removing the interiors of two disjointly and smoothly embedded copies of the disk D3 in the interior of S1 × D2."
The local-change moves used to organize the torus-fibered red edges into the disjoint arcs I and circles C, on which the only-if direction of Theorem 2 depends, are taken from the author's own preprint [11] and are not proved in the present paper. Since [11] is an unverified preprint by the same author, this is not independent support; the structural classification of the red-edge components is imported from the author's earlier work rather than established self-containedly.
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self citation load bearing
[Section 3, proof of Theorem 3, opening and local-construction paragraph]
"Here, we refer to several published articles [8, 9] and arguments. We also refer to some preprints of the author [10, 11]. ... We construct locally as in [11, (3) in STEP 2 in the proof of Theorem 2]. Or w e also construct as presented in the articles [8, 9]: for example [8, Proof o f Theorem 1.2]."
The affirmative answer of Theorem 3 is completed by delegating the decisive local Morse-Bott function constructions to the author's own prior papers and preprints rather than reproducing them here. The preprint sources [10,11] are not externally verified, and the quoted passage does not give the construction; at this load-bearing point the proof reduces to the author's earlier unverified claims, which conflicts with the paper's assertion that it is essentially self-contained.
full rationale
The central characterization in Theorem 2 has real content: the Morse-function part is anchored by Saeki's Theorem 1, and the torus-bundle extension is not identical to the definition of the admissible Morse-Bott functions. No fitted parameter is renamed as a prediction, and no displayed equation is shown to equal its own input, so there is no full self-definitional circularity. The main concerns are a correctness gap adjacent to circularity and a genuine self-citation burden. In STEP 1-2 the paper asserts, with only 'We can also check', that the preimage of each red-edge arc is a punctured lens space, S2 x S1, or S3 and that the preimage of each red-edge circle is a punctured torus bundle over S1. These assertions are exactly where torus-bundle summands enter the only-if direction, and no derivation or boundary check is supplied; for example, a red circle through a CASE 1-1-3 torus local extremum has local preimage S1 x S1 x D1 with torus boundary, not sphere boundary after removing D3's. I do not count this as a formal circular step because the preimage type is not introduced as the definition of the Reeb-data class, but it is an unproved pivotal assertion. Separately, FIGURE 2's local moves are imported from the author's preprint [11], and Theorem 3 explicitly refers to [8,9,10,11] for local constructions; these are not independent, machine-checked, or externally reproduced sources. The paper's claim to be 'self-contained in an essential way' is therefore overstated. Overall score 4: some load-bearing self-citation and an unproved pivotal assertion, but no reduction of the main theorem to its own input.
Assumptions & free parameters
assumptions (4)
- standard math Prime decomposition of closed orientable 3-manifolds (Kneser-Milnor)
- domain assumption Saeki's classification of STF Morse functions (Theorem 1 and Lemma 6.6 of [18])
- domain assumption Local regular neighborhoods of the four singular components (CASE 1-1-1 through 1-1-4)
- standard math Reeb space of a Morse-Bott function on a compact manifold is a finite graph or digraph with the prescribed vertex-edge structure
Cite this review
Pith. "Pith review of Characterizing $3$-dimensional manifolds represented as connected sums of Lens spaces, $S^2 \times S^1$, and torus bundles over the circle by certain Morse-Bott functions." pith.science (2026). https://pith.science/paper/VXOFAFFF
@misc{pith2026241211397,
author = {Pith},
title = {Pith review of: Characterizing $3$-dimensional manifolds represented as connected sums of Lens spaces, $S^2 \times S^1$, and torus bundles over the circle by certain Morse-Bott functions},
year = {2026},
howpublished = {\url{https://pith.science/paper/VXOFAFFF}},
note = {Machine review of arXiv:2412.11397}
}
abstract
We characterize $3$-dimensional manifolds represented as connected sums of Lens spaces, copies of $S^2 \times S^1$, and torus bundles over the circle by certain Morse-Bott functions. This adds to our previous result around 2024, classifying Morse functions whose preimages containing no singular points are disjoint unions of spheres and tori on $3$-dimensional manifolds represented as connected sums of connected sums of Lens spaces and copies of $S^2 \times S^1$: we have strengthened and explicitized Saeki's result, characterizing the manifolds via such functions, in 2006. We apply similar arguments. However we discuss in a self-contained way essentially.
Figures
Figures from the paper (2 more)
Reference graph
Works this paper leans on
-
[11]
N. Kitazawa, On a classification of Morse functions on 3-dimensional manifolds represented as connected sums of manifolds of Heegaard genus one , arXiv:2411.15943, 2024
arXiv 2024
-
[18]
Saeki, Morse functions with sphere fibers , Hiroshima Math
O. Saeki, Morse functions with sphere fibers , Hiroshima Math. J. Volume 36, Number 1 (2006), 141–170. MORSE-BOTT FUNCTIONS ON 3-DIMENSIONAL MANIFOLDS OF CERTAI N CLASSES 13
work page 2006
-
[1]
I. Gelbukh, A finite graph is homeomorphic to the Reeb graph of a Morse-Bot t function , Mathematica Slovaca, 71 (3), 757–772, 2021; doi: 10.1515/m s-2021-0018
doi:10.1515/m 2021
-
[2]
I. Gelbukh, Morse-Bott functions with two critical values on a surface , Czechoslovak Mathe- matical Journal, 71 (3), 865–880, 2021; doi: 10.21136/CMJ. 2021.0125-20
arXiv 2021
-
[3]
Gelbukh, Criterion for a graph to admit a good orientation in terms of l eaf blocks, Monatsh
I. Gelbukh, Criterion for a graph to admit a good orientation in terms of l eaf blocks, Monatsh. Math., 198, 61–77, 2022
work page 2022
-
[4]
Gelbukh, Realization of a digraph as the Reeb graph of a Morse-Bott fun ction on a given surface, Topology and its Applications, 2024
I. Gelbukh, Realization of a digraph as the Reeb graph of a Morse-Bott fun ction on a given surface, Topology and its Applications, 2024
2024
-
[5]
I. Gelbukh, Reeb Graphs of Morse-Bott Functions on a Given Surface , Bulletin of the Iranian Mathematical Society, Volume 50 Article number 84, 2024
work page 2024
-
[6]
Golubitsky and V
M. Golubitsky and V. Guillemin, Stable Mappings and Their Singularities , Graduate Texts in Mathematics (14), Springer-Verlag (1974)
1974
Show all 20 references
-
[7]
Hempel, 3- Manifolds , AMS Chelsea Publishing, 2004
J. Hempel, 3- Manifolds , AMS Chelsea Publishing, 2004
2004
-
[8]
Kitazawa, On Reeb graphs induced from smooth functions on 3-dimensional closed ori- entable manifolds with finitely many singular values , Topol
N. Kitazawa, On Reeb graphs induced from smooth functions on 3-dimensional closed ori- entable manifolds with finitely many singular values , Topol. Methods in Nonlinear Anal. Vol. 59 No. 2B, 897–912
-
[9]
Kitazawa, On Reeb graphs induced from smooth functions on 3-dimensional closed mani- folds which may not be orientable , Methods of Functional Analysis and Topology Vol
N. Kitazawa, On Reeb graphs induced from smooth functions on 3-dimensional closed mani- folds which may not be orientable , Methods of Functional Analysis and Topology Vol. 29 No. 1 (2023), 57–72, 2024
2023
-
[10]
N. Kitazawa, Realization problems of graphs as Reeb graphs of Morse funct ions with pre- scribed preimages , the 3rd revised version is submitted to a refereed journal b ased on positive comments, arXiv:2108.06913
-
[12]
Marzantowicz and L
W. Marzantowicz and L. P. Michalak, Relations between Reeb graphs, systems of hypersur- faces and epimorphisms onto free groups , Fund. Math., 265 (2), 97–140, 2024
2024
-
[13]
L. P. Michalak, Realization of a graph as the Reeb graph of a Morse function on a manifold . Topol. Methods in Nonlinear Anal. 52 (2) (2018), 749–762, ar Xiv:1805.06727
2018 arXiv
-
[14]
L. P. Michalak, Combinatorial modifications of Reeb graphs and the realizat ion problem , Discrete Comput. Geom. 65 (2021), 1038–1060, arXiv:1811.0 8031
2021
-
[15]
L. P. Michalak, Reeb graph invariants of Morse functions and 3-manifold groups , arXiv:2403.02291
-
[16]
Milnor, Lectures on the h-cobordism theorem , Math
J. Milnor, Lectures on the h-cobordism theorem , Math. Notes, Princeton Univ. Press, Prince- ton, N.J. 1965
1965
-
[17]
G. Reeb, Sur les points singuliers d´une forme de Pfaff compl´ etement int` egrable ou d´une fonction num´ erique, Comptes Rendus Hebdomadaires des S´ eances de I´Acad´ emiedes Sciences 222 (1946), 847–849
1946
-
[19]
O. Saeki, Reeb spaces of smooth functions on manifolds , International Mathe- matics Research Notices, maa301, Volume 2022, Issue 11, Jun e 2022, 3740–3768, https://doi.org/10.1093/imrn/maa301, arXiv:2006.0168 9
2022
-
[20]
Saeki, Reeb spaces of smooth functions on manifolds II , Res
O. Saeki, Reeb spaces of smooth functions on manifolds II , Res. Math. Sci. 11, article number 24 (2024), https://link.springer.com/article/10.1007/ s40687-024-00436-z. Institute of Mathematics for Industry, Kyushu University, 7 44 Motooka, Nishi-ku Fukuoka 819-0395, Japan, TE...
2024
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