**As** a project member or project manager
**I want to** to be able to specify negative lag
**so that** I can specify that a work package has to start a few days _before_ the finish date of another one

**Acceptance criteria**

* In the add and edit relations modal (for successors and predecessors):

* Let users enter a negative value for lag

* Negative lag only takes working days into account

* _Note: This will be challenged later with <mention class="mention" data-id="63460" data-type="work_package" data-text="##63460">##63460</mention>_

* For successors for which &#39;Working days only&#39; is off (such that they _could_ possibly be scheduled on a weekend, for example), lag will still skip non-working days.

* Eg. Assuming Sat and Sun are NWD, for a work package starting whose derived start date is Begin of the insertionnormallyEnd of the insertion on a Begin of the insertionTuesday withEnd of the insertion Begin of the deletion Tuesday,End of the deletion a Begin of the insertion0 days lag, aEnd of the insertion lag of -2 would mean that it now starts on Friday of the previous week and not Sunday.


**Related open point**

* Begin of the insertion<mention class="mention" data-id="57211" data-type="work_package" data-text="##57211">##57211</mention>

* <mention class="mention" data-id="64261" data-type="work_package" data-text="##64261">##64261</mention>End of the insertion Begin of the deletion ##57211End of the deletion