Description: Definition of the class of real vector spaces. The previous definition,
|- RRVec = { x e. LMod | ( Scalarx ) = RRfld } , can be recovered
using bj-isrvec . The present one is preferred since it does not use
any dummy variable. That RRVec could be defined with LVec in
place of LMod is a consequence of bj-isrvec2 . (Contributed by BJ, 9-Jun-2019)