On Covering Simplices by Dilations in Dimensions 3 and 4

We propose a conjecture regarding the integrally closedness of lattice polytopes with large lattice lengths. We demonstrate that a lattice simplex in dimension 3 (resp. 4) with lattice length of at least 2 (resp. 3 and no edge has lattice length 5) can be covered by dilated simplices of the form sQ, where integer s 2 (resp. 3) and Q is a lattice simplex. The covering property implies these simplices are integrally closed. As an application, we derive a simple criterion for the projective normality of ample line bundles on weighted projective spaces of dimension 3 (resp. 4). Along the way, we discover certain unexpected phenomenon.