Class that contains all elements we associate with zero, e.g. the number zero, matrices full of zero elements, or quantities of various dimension with zero magnitude. All these elements behave similarly with respect to the multiplication operator '*', but differentiation between them allows regularity in algebraic rules (e.g. dimensions of operands and product in matrix multiplication).
The product of a zero-element and anything (when the product is defined) is another zero-element (not necessarily the same). For example, if A is a 1xN matrix and B is a NxN zero matrix, then the product A*B is a 1XN zero matrix.
(Zero-Element 0) (=> (Zero-Element ?Z) (=> (Defined (* ?E ?Z)) (Zero-Element (* ?E ?Z))))