[mjul]

My guess is that it was Prolog Development Center (PDC) [1] the company behind Turbo Prolog and Visual Prolog [2]. They built a nice business providing scheduling and planning software to airlines.

They are still around if you want to get in touch.

[1] https://www.pdc.com/

[2] https://en.m.wikipedia.org/wiki/Visual_Prolog