Specification filter
Most clauses are bugs that already happened
"Write a Python function that returns Bernoulli numbers."
+ Exact arithmetic: fractions.Fraction
+ Convention: B1 = -1/2
+ Modern indexing: every index numbered
+ Zero terms: Fraction(0) for odd n > 1
+ Anchor values at named indices, B0 ... B30
+ Domain: defined for every n >= 0
Failure modes these clauses address
[not-fraction]
a spec violation
[b1-sign]
a spec violation
[ada-indexing]
a spec violation
[odd-terms]
a spec violation
[off-by-one]
a spec violation
[raises]
a spec violation
Testable candidate
Independent checks
Pass or diagnostic failure