The four-minimizer bound for homogeneous QCQPs with two constraints

Consider the homogeneous quadratically constrained quadratic optimization problem denoted by

$$. A strict local non-global minimizer is a feasible point that is a strict local minimizer but not a global minimizer. **Four-minimizer bound.** The problem$$

has at most four strict local non-global minimizers. The statement is presented after an example exhibiting four such minimizers, so the bound is sharp within the paper's discussion; its general validity is not established by the supplied text.