EntityQ1033772· pop 17· linked from 20 articlesHappy Ending problemSign in to saveproblem about proving that five points in the plane will have a subset forming the vertices of a convex quadrilateralConnectionsmathematicsEntitytriangleEntityInternational Standard Book NumberEntityintegerEntitypolygonEntityquadrilateralEntitydigital object identifierEntitypentagonEntityPaul ErdősEntityheptagonEntityEuclidean spaceEntityJSTOREntityQ118398EntityconjectureEntitybinomial coefficientEntityStirling's approximationEntityCatalan numberEntitybig O notationEntitycomplete graphEntityMathWorldEntityCategoriesDiscrete geometryEuclidean plane geometryMathematical problemsPaul ErdősPolygonsQuadrilateralsRamsey theory