Add Constraints

Constraints.md

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+Here is a list of possible constraints we may want to try to support in Dyna3. Those labeled with a ? may be unclear how to capture as a polynomial in the coordinates of the entities.
+
+- Point lies on entity
+- One entity is contained in another (For some entities, this may be (?), e.g. a point and a ball, as opposed to a sphere -- seems like that's an inequality rather than a polynomial equation.)
+- Two entities are tangent
+- Two entities coincide
+- Two entities are at a fixed distance
+- Two entities make a specific angle
+- Two entities intersect (or do not intersect (?))
+- The position of an entity is fixed to be v
+- The measure (length, area, volume, angle, dihedral angle, solid angle, ...) of an entity is fixed to be m
+- Two entities are congruent (Is this just a conjunction of some automatically-generated conjunction of some of the above?)
+- Some polynomial equation in the measures or positions of an entity or entities holds (i.e., we may want to just allow direct entry of an arbitrary polynomial constraint, e.g, `dist(a,b) + dist(b,c) =k`
+
+Definitely feel free to add items!