Planar multiple-contact problems subject to unilateral and bilateral kinetic constraints with static Coulomb friction

The contact problem in Lagrangian systems with redundant frictional bilateral and unilateral constraints and singular mass matrix. The all-sticking contacts problem

“…It is noteworthy that the sign conditions in the outwards normal cone's elements, reflect the unilaterality of the contact. Recall that K is defined in (44).…”