Type Alias: GemDirection

GemDirection = "9-to-10" | "10-to-9"

The direction of a loaded GEM file. CMS ships the forward (ICD-9→ICD-10, …_I9gem.txt) and backward (ICD-10→ICD-9, …_I10gem.txt) maps as separate, non-inverse artifacts - a forward map composed with a backward map is "not a mirror image". A GemMap therefore records which direction it is and is only ever applied in that direction.