The free pointed set on $X$ is the pointed set $\smash {X^{+}}$ consisting of:

  • The Underlying Set. The set $X^{+}$ defined by[1]

    \begin{align*} X^{+} & \mathrel {\smash {\overset {\mathclap {\scriptscriptstyle \text{def}}}=}}X\mathchoice {\mathbin {\textstyle \coprod }}{\mathbin {\textstyle \coprod }}{\mathbin {\scriptstyle \textstyle \coprod }}{\mathbin {\scriptscriptstyle \textstyle \coprod }}\text{pt}\\ & \mathrel {\smash {\overset {\mathclap {\scriptscriptstyle \text{def}}}=}}X\mathchoice {\mathbin {\textstyle \coprod }}{\mathbin {\textstyle \coprod }}{\mathbin {\scriptstyle \textstyle \coprod }}{\mathbin {\scriptscriptstyle \textstyle \coprod }}\webleft\{ \star \webright\} . \end{align*}

  • The Basepoint. The element $\star $ of $X^{+}$.


Footnotes

[1] Further Notation: We sometimes write $\star _{X}$ for the basepoint of $X^{+}$ for clarity when there are multiple free pointed sets involved in the current discussion.

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