Eikonal Equation for the Distance Function under a Smooth Nearest-Point Projection Partial Differential Equations Density of Trigonometric Polynomials Approximation Theory Universality of the Cantor Set Real Analysis Uniqueness of Limits Topology $H^1$ to $L^1$ Boundedness of Calderón--Zygmund Operators Analysis Short-Time Existence and Uniqueness for the Ricci-DeTurck Flow Analysis Calabi's Trick for Distance Function Barriers Analysis Smoothness From Fourier Coefficient Decay Harmonic Analysis Analysis Area