How to get the negative effect using -margins-

[Niels Henrik Bruun]

Dear all
Running the code (To simplify the output I've chosen to look at domestic cars in -margins-):

sysuse auto
qui regress price i.foreign##i.rep78 if rep78 > 2
margins [email protected]

I get

--------------------------------------------------------------------
                   |            Delta-method
                   |   Contrast   std. err.     [95% conf. interval]
-------------------+------------------------------------------------
     rep78@foreign |
(4 vs 3) Domestic  |   -725.519   1136.593     -3005.235    1554.198
(5 vs 3) Domestic  |  -2402.574   2164.008     -6743.024    1937.876
--------------------------------------------------------------------

However, I would like to get the effects 3 vs 4 and 3 vs 5 instead, i.e., the negatives of the above-estimated effects.
I can of course use the command -lincom- twice to get the result, but can I use margins?

[Maarten Buis]

sysuse auto
qui regress price i.foreign##i.rep78 if rep78 > 2
margins {rep78 1 -1 0}@0.foreign {rep78 1 0 -1}@0.foreign

[Hemanshu Kumar]

Maarten Buis where in the documentation can we find discussion of these ways of specifying marginlists?

[Maarten Buis]

help contrast

[Niels Henrik Bruun]

Maarten Buis : Thank you very much