/// <inheritdoc cref="GroupingAnalyzer{S,M}.Preconditions"/>
public override IEnumerable <Action <StructType> > Preconditions() =>
new[] { AnalyzersExt.AtLeastOne(Columns) }
.Concat(Columns.Select(AnalyzersExt.HasColumn))
.Concat(Columns.Select(AnalyzersExt.IsNotNested))
.Concat(base.Preconditions());