Two collars A and B may slide along two fixed rigid rods as shown. The collars are connected by another rigid rod of length l via ball$-$and$-$socket joints. a$)$ If the variables x and y are used as generalized coordinates for the system, what constraint$($s$)$ would need to be considered? b$)$ Is the constraint holonomic or non$-$holonomic? Why or why not? c$)$ How many degrees of freedom does the system have? d$)$ Derive the velocity and Pfaffian forms of the constraint.