Do not precede a sharp/flat with a redundant natural in modern notation (older-practice anti-pattern)

Older editions habitually insert a natural before an accidental of the opposite type even with nothing to cancel, purely for emphasis. Modern convention omits this as clutter.

A note with no prior accidental history for that letter/octave is authored with a natural-then-flat pair when a plain flat alone suffices.

Gould, explicit modern-practice guidance against unnecessary cautionary naturals; Read notes the older practice as a historical curiosity; Ross does not recommend it.

AGREEMENT this is an anti-pattern; RECOMMEND flagging/removing for Gradus, which teaches modern reading conventions.

Our own judgement, not a sourced convention — shown separately so the two are never confused.

This rule can be decided from pitches, durations and voices — no layout required. A validator can check it before anything is drawn.