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avoid quadratic positional access over linked-list column lists #1440

Job	Run time
Grammar Choice Conflicts	34s
Gradle Check (windows-latest)	3m 33s
Gradle Check (macos-latest)	3m 32s
Gradle Check (ubuntu-latest)	4m 22s
Maven Verify (windows-latest)	5m 32s
Maven Verify (macos-latest)	6m 17s
Maven Verify (ubuntu-latest)	4m 50s
Gradle Publish (Maven Central)	-1s
Build & Deploy Sphinx Docs	-1s
	28m 38s