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Computes the Ehrhart ring
NmzEhrhartRing(L: LIST of RINGELEM, s: RINGELEM): LIST of RINGELEM 
The exponent vectors of the given monomials are considered as vertices of a
lattice polytope
P
. The Ehrhart ring of a (lattice) polytope
P
is the monoid algebra defined by the monoid of lattice points in the cone
over the polytope
P
; see the book by Bruns and Gubeladze,
Polytopes, Rings, and Ktheory, Springer 2009, pp. 228, 229.
The function returns the generators of the Ehrhart ring. It uses the
indeterminate in the second argument as auxiliary indeterminate of the
Ehrhart ring.
/**/ Use R::=QQ[x,y,z,t];
/**/ NmzEhrhartRing([x^2,y^2,z^3],t);
[x^2*t, z^3*t, x*y*t, y^2*t]
