`Fix.TWO_PHASE_NUMBERING`

The signature `TWO_PHASE_NUMBERING`

combines the signatures `ONGOING_NUMBERING`

and `NUMBERING`

. It describes a numbering process that is organized in two phases. During the first phase, the numbering is ongoing: one can encode keys, but not decode. Applying the functor `Done()`

ends the first phase. A fixed numbering then becomes available, which gives access to the total number `n`

of encoded keys and to both `encode`

and `decode`

functions.