RationalInterval

 Verified Real Number Calculations: A Library for Interval Arithmetic
 Marc Daumas, David Lester, César Muñoz
 Cite as: arXiv:0708.3721 [cs.MS]
 https://arxiv.org/pdf/0708.3721.pdf
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 Marc Daumas, Guillaume Melquiond, Cesar Munoz.
 Guaranteed Proofs Using Interval Arithmetic. 17th IEEE Symposium on
 Computer Arithmetic, 2005, Cape Cod, Massachusetts, United States.
 IEEE, pp.188-195, <10.1109/ARITH.2005.25>. 
 HAL Id: hal-00164621 https://hal.archives-ouvertes.fr/hal-00164621
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 NASA PVS Library of Formal Developments
 https://github.com/nasa/pvslib & http://shemesh.larc.nasa.gov/fm/ftp/
 https://github.com/nasa/pvslib/blob/master/interval_arith/interval.pvs