  In a recent paper, Braun, Chung and Graham [1] have addressed a
single-processor scheduling problem with time restrictions. Given a fixed
integer $B \geq 2$, there is a set of jobs to be processed by a single
processor subject to the following B-constraint. For any real $x$, no unit time
interval $[x, x+1)$ is allowed to intersect more than $B$ jobs. The problem has
been shown to be NP-hard when $B$ is part of the input and left as an open
question whether it remains NP-hard or not if $B$ is fixed [1, 5, 7]. This
paper contributes to answering this question that we prove the problem is
NP-hard even when $B=2$. A PTAS is also presented for any constant $B \geq 2$.
