= Solution
\b[Endpoint energies, endpoint phase patterns and a conserved <symmetry> fix the qualitative connectivity.] Each initial orbital must end in the appropriate product <symmetry> block, and the ordering within a generic block is preserved by avoided crossings. The two singleton blocks $A_2$ and $B_2$ have unique partners. No numerical calculation at each intermediate separation is required to draw those connections.
This conclusion is limited to a correlation diagram: it does not determine intermediate orbital energies, interaction strengths, the location or height of a <reaction energy barrier>, or the lowest route on a multidimensional <potential energy surface>. If the reaction breaks the assumed <symmetry>, previously distinct <symmetry> blocks can mix and the diagram must be reconsidered.
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