Uniqueness of tangent flows

A mean curvature flow develops tangent flows by rescaling near a singularity. A sequence of rescaling factors is a sequence $\lambda_i\to\infty$ used to obtain a blowup limit. Uniqueness of tangent flows. Tangent flows are independent of the choice of sequence of rescaling factors $\lambda_i\to\infty$. This is a fundamental open problem; in the setting discussed, it would follow from the rigidity of the round cylinder, and direct approaches are also possible.