  It has been recently pointed out by Caves, Fuchs, and Rungta that real
quantum mechanics (that is, quantum mechanics defined over real vector spaces
provides an interesting foil theory whose study may shed some light on just
which particular aspects of quantum entanglement are unique to standard quantum
theory, and which ones are more generic over other physical theories endowed
with this phenomenon. Following this work, we discuss some entanglement
properties of two-rebits systems, making a comparison with the basic properties
of two-qubits systems, i.e., the ones described by standard complex quantum
mechanics. We also discuss the use of quaternionic quantum mechanics as applied
to the phenomenon of entanglement.
