Wigner type theorems for projections


                       Georges Chevalier 


                     (Univ. Lyon I, France)


Abstract : We present an algebraic definition of continuous
projections (=idempotent) defined on a topological vector space and
describes the form of all bijective transformations on the set of
rank-one projections which preserves orthogonality in both
directions. This result generalizes a theorem of L. Molnar related to
projections in Banach spaces.