Relation of equivalence between the bipoints of a geometric plane so that any bipoints (

*a*,*b*) and (*c*,*d*) in a plane where*a*≠*b*and*c*≠*d*, (*a*,*b*) and (*c*,*d*) are said to be equipollent if and only if*ab*and*cd*are the opposite sides of a parallelogram.