It is immaterial if there is an actual taxon to which the automatically established name applies; if ever such a taxon is recognised, there is a name available for it. This is the principle that in cases of conflicts between simultaneously published divergent acts, the first subsequent author can decide which has precedence. It supplements the "principle of priority", which states that the first published name takes precedence. The principle of the first reviser deals with situations that cannot be resolved by priority. These items may be two or more different names for the same taxon, two or more names with the same spelling used for different taxa, two or more different spellings of a particular name, etc. In such cases, the first subsequent author who deals with the matter and chooses and publishes the decision in the required manner is the first reviser, and is to be followed. Example:  Linnæus 1758 established "Strix scandiaca" and "Strix noctua" (Aves), for which he gave different descriptions and referred to different types, but both taxa later turned out to refer to the same species, the snowy owl. The two names are subjective synonyms. Lönnberg 1931 acted as first reviser, cited both names and selected "Strix scandiaca" to have precedence. This is the principle that the name of each taxon must be unique. Consequently, a name that is a junior homonym of another name must not be used as a valid name. It means that any one animal name, in one particular spelling, may be used only once (within its group). This is usually the first-published name; any later name with the same spelling (a homonym) is barred from being used. The principles of priority and first reviser apply here. For family-group names the termination (which is rank-bound) is not taken into account. Genera are homonyms only if exactly the same — a one-letter difference is enough to distinguish them. Examples:  In species, there is a difference between primary and secondary homonyms. There can also be double homonyms (same genus and species). A slight difference in spelling is tolerated if Article 58 applies. "Primary homonyms" are those with the same genus and same species in their original combination. The difference between a primary junior homonym and a subsequent use of a name is undefined, but it is commonly accepted that if the name referred to another species or form, and if there is in addition no evidence the author knew that the name was previously used, it is considered as a junior homonym.