= Nonequivalent p-s and p-p term counting
For electrons in distinct radial orbitals, angular coupling permits all $L$ from $|l_1-l_2|$ to $l_1+l_2$ and both total <spins> $S=0,1$. A p-s pair therefore gives singlet and triplet P terms. A nonequivalent p-p pair gives singlet and triplet S, P and D terms. The equivalent-subshell exclusion restrictions do not remove these nonequivalent terms. Counting $(2S+1)(2L+1)$ gives 12 p-s and 36 p-p microstates, matching products of one-electron state counts.
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