Test whether two compatible scalars are equal.

Return the exact number of sites in finite DOMAIN. This deliberately says nothing about coordinate or offset representation. Those mappings belong to concrete domain protocols and are added only when a client needs to traverse them.

Return an immutable keyword domain preserving MEMBERS' order exactly. Duplicate or non-keyword members are rejected. The resulting mapping is appropriate for dense runtime columns and for explicit persisted vocabulary tables; the keyword is semantic identity and its offset is only meaningful under this domain.

Return KEYWORD's dense offset under DOMAIN. When ERROR-P is false, return NIL for a keyword outside the domain.