// This is probably for use in Meta_v2 to get the most efficient
// (read compact) implementation of typical meta scenarios.

interface MutatingMap<A, B> {
  Non-mutating:
  
    isEmpty
    size
    entrySet/iterator (I prefer the latter)
    contains
    hashCode/equals (of course)
    
  Mutating:
  
    put
    remove
    putAll etc
    
  
  
}