Clifford-like parallelisms

Abstract

Given two parallelisms of a projective space we describe a construction, called blending, that yields a (possibly new) parallelism of this space. For a projective double space $(\mathbb{P},\parallel_\ell,\parallel_r)$ over a quaternion skew field we characterise the "Clifford-like" parallelisms, i.e. the blends of the Clifford parallelisms $\parallel_\ell$ and $\parallel_r$, in a geometric and an algebraic way. Finally, we establish necessary and sufficient conditions for the existence of Clifford-like parallelisms that are not Clifford.