#1293 combine_rel and first_rel .. sixteenth_rel; combine_data checks its relations against the factors New page combine_rel, for the relations back from a combined unit to its factors, per element. combine_data: since 20.24.0 one relation per factor directly, the check against the factors and what it does not catch, null for a value outside its factor; the example column NHCityYear_rel had the first factor varying fastest (0, 3, 4, 2, 5) and now reads 0, 1, 3, 4, 5, as the engine numbers. combine: sixteen factors at most, not six; the sub-item twelveth_rel is twelfth_rel; first_rel(x_rel) instead of X/first_rel[x_rel] for large domains. combine_unit_uint8_16_32_64 and Relational functions link to the new page. The new page is not yet in the website menu, nav/geodms.md of GeoDmsWikiToStaticHtml.