Description of the problem on p.318: A circle of diameter 2 is initially centered at $(0,0)$, and it is moving with the velocity 1 along the x-axis. The square has side-length 2, and is initially centered at $(0,-8)$, and is moving with the velocity [vx] and [vy]. We want to decide if these two objects would collide.
load redlog; rlset ofsf;
vx, vy: velocity of the square.
pcol := ex({tt,x,y},
tt>0 and -1<=x-vx*tt<=1 and -9<=y-vy*tt<=-7 and (x-tt)**2+y**2<=1);
refined sentence (p.319) adding necessary condition for the collision time:
col := ex({tt,x,y},
6<=vy*tt<=10 and -1<=x-vx*tt<=1 and -9<=y-vy*tt<=-7 and (x-tt)**2+y**2<=1);
selection for vx, vy on p.318:
vx := vy := 17/16;
rlqe col;
selection on p.325:
vx := vy := 15/16;
rlqe col;
end; % of file