I have a vague memory that this relationship is possible, but I can't think of any examples off the top of my head. Is there a canonical or common example(s)?

I am imagining that in two independent experiments, increasing input B leads to an increase in output A, and the same for input C. But if both inputs B and C are increased together, that this causes a reduction in output A. I think this kind of relationship would be most likely due to an interaction of B and C, i.e. a `B*C` term in the equation for A. It could be caused by an additional hidden variable.

What would be the correct terminology for this relationship? Is it simply non-linear? Or multivariate non-linear? Or...?