nLab plus construction

The terminology ‘plus construction’ is used for three very different types of construction.

• The version which sends a presheaf to a separated presheaf to a sheaf is described at plus construction on presheaves and sheaf.

• The process of killing a perfect normal subgroup of the fundamental group of a space is described under Quillen plus construction.

• The assignment, due to John Baez and James Dolan, $O \mapsto O^+$ sending a operad (with colours $S$) to a new operad whose algebras are $S$-coloured operads equipped with an operad morphism to $O$ (i.e. slices over $O$).

References

• John Baez, James Dolan, Higher-dimensional algebra III: $n$-categories and the algebra of opetopes, Adv. Math. 135 (1998), 145–206. (arXiv:q-alg/9702014)