Both rails from one blueprint

The failure where a two rail check builds both rails from the same field list, the same parse, or the same helper, so it compares values to themselves. Agreement is then guaranteed and proves nothing. Independence has to go all the way down, and shared logic is disclosed and counted as a single read.

Principle 2 · Two independent reads beat one careful one

Where does Both rails from one blueprint come from?

Principle 2 of the Kymira doctrine, Two independent reads beat one careful one. Both rails from one blueprint is the name the doctrine gives to what that principle requires in practice.

What failure is Both rails from one blueprint named after?

Both rails from one blueprint. A "two independent reads" verification that built both reads from the same field list and compared 537 values to themselves. Agreement guaranteed, meaning zero.

What does it look like on a real file?

A two rail check built from one field list compared 537 values to themselves and agreed on every one, in our own audits.

Not for

Not a naming problem. Renaming the second rail changes nothing; only different logic all the way down counts as a second read.

Nearest terms

Dual railComputing a published value twice by two routes that share as little logic as possible: once...Borrowed evidenceTwo or more checks citing the same fire test log as proof, so one captured red run stands in...Fire-test theaterA test that re-implements the guard's comparison inline instead of calling the deployed guard

Last updated 2026-09-02 · Dylan, founder · one of 40 terms in the Kymira glossary, each one named after something we watched go wrong in a real build or in our own audits.

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