> The Fusion sketch solver is badly compromised, it can't do more than two or so simple successive Tangent relations without bugging out. And, my experience with Solidworks is the same, not sure if this is still true.

In my experience of building a sketcher at D-Cubed for a consultancy client (1995-2000) on top of D-Cubed's DCM, this is because DCM's curves (which are unbounded BTW) are not directed so that there are lots of erroneous solutions to attempting to constrain G1 chains of tangent bounded curves. For example the Apollonius Problem [1][2] of 3 tangent circles/lines has 2^3 = 8 solutions. IMO if John Owen had chosen directed curves for DCM then dragging configurations of tangent circles would be more stable.

I'll end with a quote from the Preface of Julian Lowell Coolidge's 1916 "A Treatise on the Circle and the Sphere" [3]:

> Among the cartesian theorems there is a sharp sub-division between those where the radius is looked upon as essentially signless and those where a positive or negative radius is allowed.

[1] https://mathworld.wolfram.com/ApolloniusProblem.html

[2] https://observablehq.com/@d3/apollonius-problem#

[3] https://en.wikipedia.org/wiki/A_Treatise_on_the_Circle_and_t...