  We show NP-completeness for several planar variants of the monotone
satisfiability problem with bounded variable appearances. With one exception
the presented variants have an associated bipartite graph where the vertex
degree is bounded by at most four. Hence, a planar and orthogonal drawing for
these graphs can be computed efficiently, which may turn out to be useful in
reductions using these variants as a starting point for proving some decision
problem to be NP-hard.
