Is flat rotation curve a sign of cosmic expansion?

Four alternative proposals as the possible solutions for the rotation curve problem are introduced on the basis of assumption that the cosmic expansion is engaged with the Galactic dynamics over the halo. The first one proposes a modification of equivalence principle in an accelerating Universe. The second one proposes a modification of the Mach principle in an expanding universe. The third one proposes a dynamics of variable-mass system for the halo in an expanding universe, and the fourth one proposes the replacement of physical radius with comoving one over the halo, in an expanding universe.