parallel projectivity
1Projective plane — See real projective plane and complex projective plane, for the cases met as manifolds of respective dimension 2 and 4 In mathematics, a projective plane has two possible definitions, one of them coming from linear algebra, and another (which is… …
2Admissible rule — In logic, a rule of inference is admissible in a formal system if the set of theorems of the system is closed under the rule. The concept of an admissible rule was introduced by Paul Lorenzen (1955).DefinitionsThe concept of admissibility, as… …
