To most effectively contain a demon, a summoning circle is drawn along equipotential lines. These are specific to each demon - if you know the demonic field equations, you can reconstruct a circle from a sigil and vice versa.
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Three-dimensional demons, you contain with circles. Four-dimensional demons, you build complicated brass spheres for, five-dimensional ones you trap with constantly moving orreries of these.
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To summon a demon together with its counter-aspect, use a lemniscate. Or rather, don't, or have a plan for separating them very quickly, since they will try to annihilate each other with extreme prejudice.
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