In geometry, [b]Dini's surface[/b] is a surface with constant negative [b]curvature[/b] that can be created by twisting a [b]pseudosphere[/b]. It is named after [b]Ulisse Dini[/b] and described by the following [b]parametric equations[/b]:[br][br] x=a cos(u) sin(v)[br] y=a sin(u) sin(v)[br] z=a (cos(v) + ln(tan(v/2)))+b u [br][br]Surface[ <Expression>, <Expression>, <Expression>, <Parameter Variable 1>, <Start Value>, <End Value>, <Parameter Variable 2>, <Start Value>, <End Value> ][br][br]c = Surface[((a * cos(u)) * sin(v)), ((a * sin(u)) * sin(v)), (a * (cos(v) + log(tan((0.5 * v))))) + (b * u), u, 0, 12.566370614359172, v, 0.01, 2]