The two infinite series are familiar. Algebraically, each series by itself is equal to (1 + z) n, for
all z, since the result of multiplying each series by the finite polynomial (1 + z) -n is 1. If one
further considers convergence, each converges to (1 + x) n, the radius of convergence for the first
series being Ixl < 1, while that for the second series is Izl > 1. Besides this somewhat puzzling
result, thinking of the variable r as looping out to infinity and returning to the negative side also
suggests thinking of the variable n as doing the same. Then one can think of the rows for n > 0
as being the "top half' of Pascal's
the (o) forming the lefthand edge
n = -1 forming the bottom edge.
lattice points (~) are situated and
triangle and those for n < 0 as being the "bottom half," with
of the triangle, the (n ) forming the righthand edge, and row
Effectively, this means taking the infinite plane on which the
rolling it up into an infinite torus.