A legal drawing is defined by (a) legal arcs or (b) legal areas. The rules for legal arcs and areas are:
Rule 3. Each legal arc must be a segment of a legal circle.
Rule 4. At both endpoints of a legal arc, some legal circles must touch or intersect.
Rule 5. The arc width of a legal arc must be equal to the radius of some legal circle.
Rule 6. A legal area is an area whose border is a closed chain of legal arcs. Legal areas may be shaded using a small set of grey levels.