Words / CONCEPT

AdaptiveMergePrefix

For an arbitrary additive commutative group, a word is Good exactly when every nonempty proper contiguous interval has nonzero sum. Equality of prefixes at i < j is permitted only for i = 0 and j = length. The entire word may have sum zero. The prefixSum and ProperIntervals names transparently use SeparatedPrefixReflection.pref and Good. The equivalence directly consumes that original module's good_iff, with no finite-ambient, torsion, nonzero-total, strict-cone or separation assumption. This consumed adapter supplies no new mathematical content.