INTERFACE FOR TRIANGLES
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triangle = Triangle(x1, y1, x2, y2, x3, y3)
triangle = Triangle(point1, point2, point3)
triangle = Triangle()   # Triangle(0, 0, 1, 0, 0, 1)
repr(triangle)   # return string
hash(triangle)
triangle.copy()   # return triangle
triangle.area()
triangle.center()   # return point
triangle.make3()    # return three smaller triangles
triangle.make4()    # return four smaller triangles
triangle.move(x, y)   # return new triangle
triangle.move(point)   # return new triangle
t1 == t2, t1 != t2
point in triangle   # return bool
segment in triangle   # return bool
triangle.orientation()   # return +1|0|-1
t1.common_segment(t2)   # return segment
triangle.third_node(point1, point2)   # return a third point
triangle.circumcenter()   # return point
triangle.in_circumcircle(point)   # return bool
triangle.iterpoints()   # counterclockwise
triangle.itersegments()   # segment.pt1 < segment.pt2
triangle.itersegments_oriented()   # the face is on the right
triangle.gnu()   # return gnuplot string
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EOF
