Email addresses:   local @ domain

Variable lengths, up to 128 chars, case-insensitive

Operators:   = same,   > greater (dom,loc),   ~ same domain,   etc.

Support btree index and hashed files

Local      ::= NamePart NameParts
Domain     ::= NamePart '.' NamePart NameParts
NamePart   ::= Letter | Letter NameChars (Letter|Digit)
NameParts  ::= Empty | '.' NamePart NameParts
NameChars  ::= Empty | (Letter|Digit|'-') NameChars

Need: storage structure, in/out/operator functions, operator classes