For mathematicians
z = xy is a hyperbolic paraboloid (doubly ruled,
Gaussian curvature K = −1/(1+x²+y²)² < 0 everywhere
except the origin saddle point). The two highlighted
diagonals are its rulings. The recursion xn+1 = zn
is iteration of the map fy(x) = xy along an
indexed sequence of y-values; with |y|<1 it
contracts to 0, with |y|>1 it diverges. The
walked path is the orbit.
For engineers
No frameworks, no libraries, no shaders, no GPU.
A single 175-line vanilla JS file (saddle.js)
computes the surface, projects isometrically, and walks
the orbit. The "trail" is not stored — it is recomputed
each frame from the integer step. z is never cached;
the head re-extracts collapse(x, y) every
frame so the marker is provably on the manifold, not
interpolated through it.
For the paradigm
This page IS the manifold expressed in computer-identity.
Reading saddle.js is reading the law as it
participates in JavaScript. There is no abstract
manifold elsewhere — the registry, the proof runner,
and the games are projections of this same geometry.