Hi Ali,

Your statement is true. Indeed,

if ∀(x,y,z) ∈ D: A(x,y,z)+B(x,y,z)=C=const, (*)

and ∀(x,y,z) ∈ L⊂D: A(x,y,z)=m=const,

then from (*) ∀(x,y,z) ∈ L: B(x,y,z)=C-m=const.

Dear Dr. Adlucky

Thanks for your reply.

https://www.sciencedirect.com/search/advanced?qs=Coincidence%20of%20two%20contour%20maps&show=25&sortBy=relevance