has member has member has_member_count sequence feature set 'Sets' are used to represent entities that are typically collections of more than one member. But we allow for sets that contain 0 members (an 'empty' set) or 1 member (a 'singleton' or 'unit' set), consistent with the concept of 'mathematical sets'. Sets may also include duplicates (i.e. contain more than one member representing the same feature). The notion of a 'complement' is a special case of a set, where the members necessarily comprise an exhaustive collection of all objects that make up some well-defined set. It is useful for defining many biologically-relevant sets of sequence features. For example, a 'haplotype' is the set of all genetically-linked alleles on a single chromosomal strand at a defined location - e.g. the SNP alleles {rs7412-C, rs429358-C} comprise the haplotype defining the APOEɛ4 gene allele [1]. And a 'single locus complement' is the set of all alleles at a specified location in a particular genome - e.g. the APOEɛ4 and APOEɛ4 gene alleles ([1], [2]) that make up the 'Gs270' APOE genotype [3]. [1] https://www.snpedia.com/index.php/APOE-%CE%B54 [2] https://www.snpedia.com/index.php/APOE-%CE%B52 [3] https://www.snpedia.com/index.php/Gs270 1. The set of all alleles at a particular location in a genome (a 'single locus complement') - e.g. {APOE-epsilon2 / APOE-epsilon4} at the APOE locus 2. The set of all alleles that comprise a haplotype - e.g. the SNPs {rs7412-T, rs429358-T} in the APOEɛ2 allele. 3. The set of all chromosomes in a genome - e.g. {human Chr1, 2, 3, . . . 22, X, Y} A set of sequence features. sequence feature or set sequence_feature