Hyperbolic geometry or hypercycle, then the triangle has no circumscribed circle. As in spherical and elliptical geometry, in hyperbolic geometry if two triangles are similar, they must be congruent. A special polygon in hyperbolic geometry is the regular apeirogon, a uniform polygon with an infinite number of sides. In Euclidean geometry, the only way to construct such a polygon is to make the side lengths tend to zero and the apeirogon is indistinguishable from a circle, or make the interior angles tend to 180 degrees and the apeirogon approaches a straight line. However, in hyperbolic geometry, a regular apeirogon has sides of
OMB Circular A-21 OMB Circular A-21 OMB Circular A-21 is a Government circular that sets forth the rules governing the eligibility and calculation of costs in support of sponsored research, development, training and other works produced in agreement with the United States Federal Government, but does not attempt to identify or dictate agency or institutional participation in those works. The last revision is dated May 10, 2004. This circular is divided into ten sections: This section outlines the principles and policies that must be followed regarding the accounting principles, arrangements, and exemptions for any training or work produced under the contract as agreed