A handful of mathematical structures run under your stack in different costumes: a trade-off that is really a filter, an independence that only holds on calm days, a swarm whose parts quietly start feeding each other. Name the shape under a belief and you inherit the test the field that met it first already built. A candidate diagnosis, not a verdict.
Write the load-bearing assumptions in your work: a trade-off you design around, an independence you rely on, a set of parts you trust not to pull each other along. Start with the one that would cost you most if it turned out to be an artefact of how you measured it.
Name the shape under each one and its verdict appears as you go. New here? to watch it work.
The three questions, to keep
Filter test. Found a trade-off? Ask what you filtered on. If you only see it inside a group that got in by clearing one bar or the other, part of it lives in the filter rather than the world. That is a collider.
Extreme test. Relying on two things being independent? Ask what they do on the worst day, not the average one. The calm-weather number lies first. That is tail dependence.
Loop test. Are the parts coupled through shared state? If one part changes an environment the others respond to, you have a loop, and agreement compounds without ever being independently earned. Damp the loop; do not vary the parts. That is resonance.
One structural lens at a time, with the sourcing shown. Essays and runnable instruments, free.
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