Tutorial Post 15: Sets.

As noted in Tutorial Post on Data Organisation,  each endpoint has a set attribute. Endpoints are grouped into disjoint sets. The set attribute is just an index of the endpoint's group. There is also a 'current set index', which indicates one of the set indices.

Sets are useful for logical grouping of the endpoints.

• If the endpoints from different sets have the same position, then you can select only endpoints from the current set by pressing: 'QSS' ("ADD ENDPOINTS FROM THE CURRENT SET TO SELECTION" on Selection Menu).
• On the other hand, if you have some endpoints selected, then you can create a new set that contains only the selected endpoints, extracting them from their old sets ('QSE') ("EXTRACT THE SELECTED ENDPOINTS TO A NEW SET" on Selection Menu).
• If you created the copy of selectde endpoints ('QDC...'), then the copies of the  endpoints are placed in a new set. (The glue elements have endpoints in distinct sets.) 
• If you merge from a file ('QFM') then the sets of the merged endpoints are separate from the existing sets (while all the merged endpoints are selected and you can extract them to a single set if you wish) 

Set Menu is invoked by key sequence: 'QN'

I this menu you can change the current set and restrict visibility to the elements that have all the endpoints in (are included in)  the current set or to the elements that have at least one endpoint in (are incident to) the current set.

In the example we have copied two white segments from set 0  (with segment glues between endpoints).
The copy has been moved and painted red.
The copied endpoints have been automatically placed in new set (set 1).
The endpoints of set one have been selected with key sequence 'QSS', when the current set index was 1, and then bookmarked with 'QSB'.
Then the current set index was changed to 0 (by repeating 'QNN') and the endpitoints of set 0 (current set) have been selected ('QSS').

After pressing 'QN0'  we would see the elements included in current set:

If we pressed 'QN1' then we would see the elements incident to the current set:

(Note that now the glues are also visible.)

We can also display some statistics with 'QNP':

You may also cycle with through the available set indexes and view restrictions, by pressing just the key 'N'.

Note that the set attributes of the endpoints may change  their values while you are not watching, since mki3d tries to minimize the total number of available set indexes, by ensuring that the only index of an empty set is the maximal index. After all, the set attributes are only used to indicate the partitioning of the endpoints, and we do not want to cycle through many empty groups, nor to remember the index numeric values.