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A straight line segment can be drawn joining any two points
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Any straight line segment can be extended indefinitely in a straight line
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Given any straight line segment, a circle can be drawn having the segment as radius and one endpoint as center
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All right angles are congruent
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If two lines intersect a third in such a way that the sum of the inner angles on one side is less than two right angles, then these two lines must intersect on that side if extended far enough