Generally, or specifically, is there any licensing issue with using any of the well known lighting/reflectance models (i.e. the BRDFs or other distribution or approximation functions):

Phong, Blinn–Phong, Cook–Torrance, Blinn-Torrance-Sparrow, Lambert, Minnaert, Oren–Nayar, Ward, Strauss, Ashikhmin-Shirley

and common modifications where applicable, such as:

Beckmann distribution, Blinn distribution, Schlick's approximation, etc.

in your shader code utilised in a commercial product? Or is it a non-issue?