Use of stong and rubber constraint

Hi, i’ve read the scheduler documents. So i have questions: i saw that with a rubber constraint, for example type finish-start, i can’t assign a lead to the predecessor. So if i want to enlight possible leads or lags on a predecessor, i basically must use strong constraints, that is the normal constrain.Is it correct? Thanks and regards.

I am not quite sure that I understand the question, sorry.

i can’t assign a lead to the predecessor

If you use “lead” and “lag” as defined here: What are lead and lag time in project management? - QRP International

then why can’t you assign lead/lag for a rubber dependency? It works fine. If you move the predecessor task forward, the successor will be scheduled to start taking into account the lag, if rescheduling is necessary. It may not be necessary if the successor already starts way later than the predecessor finishes.

i want to enlight possible leads

Can you please clarify the word “enlight” in this context, if it matters?

Yes i mean lead as negative delay in finish-start strong link, and lag as positive delay.

In elaborazione: 17171703832068136504266803412730.jpg…
This is an example of lead

This is lag

Enlight means “to make evident and keep trace”

So what is the issue? You can create positive and negative lags regardless if the dependency is strong or rubber. They work and reschedule the tasks so that the following were true:

// for strong dependencies
predecessor_end + lag = successor_start 

// for rubber dependencies
predecessor_end + lag <= successor_start

I understand, but if you see the attachments, you’ll find that the same lead works for strong and not for rubber link. This is the point i can’t understand.

Because the constraint is already satisfied:

predecessor_end + lag <= successor_start

June 21 - lead < June 24