Theorem 5.5.2 (Group completion theorem, telescope form). Let \(M\in \CMon (\An )\) and let \(x\colon *\to M\) be a point. Assume that:
- (1)
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The class \([x]\) generates the commutative monoid \(\pi _0(M)\);
- (2)
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Each path component of \(T(M,x)\) has abelian fundamental group.
Then the comparison map \[ \gamma _{M,x}\colon T(M,x)\to M^{\grp } \] is an isomorphism of animae.
Proof. Under assumption (1), the singleton \(\{[x]\}\) is a generating set for \(\pi _0(M)\), and \(T(M,x)\) is the object denoted \(M_{\infty }\) by Nikolaus. The claim is therefore the implication (4) \(\Rightarrow \) (3) of Nikolaus (2017), Proposition 6. โก
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