https://www.physicsforums.com/threads/has-it-ever-been-proven-or-disproven-that-a-coincident-set-of-mutual-inductances-are-always-conserved.1048229/



sqrt{1 – \left( {\sqrt{5} – 1} over {2} \right) } = {\left( {\sqrt{5} – 1} over {2} \right)} ^ 2 ≈ 38 per cent