@article {MR2794560,
	title = {Angles in {$C^\ast$}-algebras},
	journal = {Houston J. Math.},
	volume = {37},
	number = {2},
	year = {2011},
	pages = {501{\textendash}517},
	issn = {0362-1588},
	author = {Anoussis, M. and Katavolos, A. and Todorov, I. G.}
}
