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In Coalgebras in symmetric monoidal categories of spectra, Péroux and Shipley prove the following (Lemma 2.4):

Let $\mathcal{C}=\mathsf{Sets},\mathsf{Top}$, or $\mathsf{sSets}$. The free basepoint functor $$(-)^+\colon(\mathcal{C},\times,\mathrm{pt})\to(\mathcal{C}_*,\wedge,S^0)$$ lifts to an equivalence of categories $$(-)^+\colon\mathsf{CoMon}(\mathcal{C})\dashrightarrow\mathsf{CoMon}(\mathcal{C}_*).$$ As such, any comonoid in $\mathcal{C}_*$ is isomorphic to one of the form $(C^+,\Delta^+_{C},\epsilon^+_C)$ with $(C,\Delta_{C},\epsilon_C)$ a comonoid in $\mathcal{C}$.

  • Is this result valid in general for $\mathcal{C}$ a bicomplete Cartesian closed symmetric monoidal category, where $(\mathcal{C}_*,\wedge,S^0)$ is now the symmetric monoidal category in Riehl, Categorical Homotopy Theory, Construction 3.3.14?
  • Let $\mathcal{C}$ be a bicomplete Cartesian closed symmetric monoidal $\infty$-category.
    1. Can we similarly build a symmetric monoidal $\infty$-category structure $(\wedge,S^0)$ on the category $\mathcal{C}_*$ of pointed objects of $\mathcal{C}$ (i.e. the coslice $\infty$-category $\mathcal{C}_{*/}$)?
    2. If this is the case, do we have an analogue of Péroux–Shipley's result for $\mathbb{E}_{k}$-comonoids in $(\mathcal{C}_*,\wedge,S^0)$, where $1\leq k\leq\infty$?
    3. (If Item 1 fails, is Item 2 nevertheless true for $\mathcal{C}=\mathcal{S}$, the $\infty$-category of spaces?)
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  • $\begingroup$ I am confused by your reference to my comment. I was talking about $E_k$-monoids, and here you seem to be talking about $E_k$-comonoids... $\endgroup$ Commented Aug 10, 2021 at 22:05
  • $\begingroup$ @DenisNardin sorry, I completely misunderstood your comment (and have reverted the edit back). Thanks! $\endgroup$
    – Emily
    Commented Aug 11, 2021 at 12:54
  • $\begingroup$ An update: Maximilien replied to my question in email: 1) Lemma 2.4 is valid for all $(\mathcal{C}_*,\wedge,S^0)$; 2) One can carry this construction over to the $\infty$-setting too; 3) The analogue of his result with Shipley is true for $\mathcal{S}_*$, and in fact also for any $\infty$-topos. $\endgroup$
    – Emily
    Commented Aug 11, 2021 at 21:58

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