['The', 'Aναβ', 'equation', 'of', 'motion', 'leads', 'to', '(', '3)εμναβ∂βw−−FγδaFaγδ=0', ',', 'which', 'is', 'then', 'integrated', 'to', '(', '4)w=−FμνaFaμν+M.', 'It', 'is', 'easy', 'to', 'verify', 'that', 'the', 'Aaμ', 'equation', 'of', 'motion', 'leads', 'us', 'to', '(', '5)∇μFaμν+MFaμν−FαβbFbαβ=0', '.']