PlanetPhysics/Thin Double Track

Let us consider a [[../PiecewiseLinear/|square]] map $u:I^2⟶X$ in a [[../CoIntersections/|topological]] space $X$. Then the [[../ThinEquivalence/|homotopy]] class of $u$ relative to the [[../PiecewiseLinear/|boundary]] $\partial I^2$ of $I$ is called a {\it double track}. A double track is {\it thin} if it has a thin representative.