The Bianchi-Bäcklund transform leads to more and more complicated, but
explicit, solutions q(u,v) of the Sine-Gordon Equation (SGE). Each SGE
solution determines a parametrized surface F(u,v)
with Gauss curvature
K = -1
.
In spite of the sharp rims these surfaces are defined for all (u,v)
in R^2. The singular rims occur in a similar way as the cusps of rolling
curves: At the zeros of sin(q(u,v))
the velocity of one set
of parameter lines becomes zero and the parameter lines reverse their direction,
so that each produces a cusp and all these cusps are a rim.