The requirement of a sufficiently positive impact angular velocity
is intuitively clear, but the grazing scenario seems so unlikely that
we choose to ignore it. Hence strict inequality as in the third
condition of (20) will be used. It is also of interest to note that the
problem in which the ball simultaneously impacts both floor and
wall in the corner is indeterminate within the context of the
model. Essentially there are seven unknowns in the impact,
namely four impulsive force components, two at each point of
contact, and the three velocity components after the bounce.
Whilst seven equations, four of restitution and three moment
equations, can be written down, it is found that they are not
consistent. Hence the ball is unable to respond simultaneously at
the two distinct points of contact.