The subject of counting positive lattice points in n-dimensional simplexes
has interested mathematicians for decades due to its applications in singularity the-
ory and number theory. Enumerating the lattice points in a right-angled simplex is
equivalent to determining the geometric genus of an isolated singularity of a weighted
homogeneous complex polynomial. It is also a method to shed insight into large gaps
in the sequence of prime numbers. Seeking to contribute to these applications, in this
paper, we prove the Yau Geometric Conjecture in six dimensions, a sharp upper bound
for the number of positive lattice points in a six-dimensional tetrahedron. The main
method of proof is summing existing sharp upper bounds for the number of points in
5-dimensional simplexes over the cross sections of the six-dimensional simplex. Our new
results pave the way for the proof of a fully general sharp upper bound for the number
of lattice points in a simplex. It also sheds new light on proving the Yau Geometric and
Yau Number-Theoretic Conjectures in full generality.