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Published online by Cambridge University Press: 20 November 2018
The $H$-space that represents Brown-Peterson cohomology $\text{B}{{\text{P}}^{k}}\left( - \right)$ was split by the second author into indecomposable factors, which all have torsion-free homotopy and homology. Here, we do the same for the related spectrum $P\left( n \right)$, by constructing idempotent operations in $P\left( n \right)$-cohomology $P{{(n)}^{k}}\left( - \right)$ in the style of Boardman-Johnson-Wilson; this relies heavily on the Ravenel-Wilson determination of the relevant Hopf ring. The resulting $\left( i\,-\,1 \right)$-connected $H$-spaces ${{Y}_{i}}$ have free connective Morava $K$-homology $k{{(n)}_{*}}({{Y}_{i}})$, and may be built from the spaces in the $\Omega$-spectrum for $k\left( n \right)$ using only ${{v}_{n}}$-torsion invariants.
We also extend Quillen's theorem on complex cobordism to show that for any space $X$, the $P{{\left( n \right)}_{*}}$-module $P{{(n)}^{*}}\,(X)$ is generated by elements of $P{{(n)}^{i}}(X)$ for $i\,\ge \,0$. This result is essential for the work of Ravenel-Wilson-Yagita, which in many cases allows one to compute BP-cohomology from Morava $K$-theory.