Explanation B4:

The dimensionality as observed from the residue curve is 1. This result is explained by the constrained motion of the two upper arms of the hands as they are only allowed to move horizontally,hence both upper arms are governed to the constraint. Mathematically,

For first hand:
L*cos(theta1)+L*cos(theta2)=x;
L*sin(theta1)+L*sin(theta2)=y;

For second hand:
D+L*cos(theta3)+L*cos(theta4)=x';
L*sin(theta3)+L*sin(theta4)=y;

Therefore =>sin(theta3)+sin(theta4)=sin(theat1)+sin(theta2);
Also y is constant so 	theta2=f(theta1);
			theta3=f(theta4);
			theta3=f(theta1);

Therfore three angle is directly dependent on one angle. Hence one degree of freedom is completely justified. As compared to problem B2 where the hands move randomly,there is no such constraint and all angular motions are independent,therefore its DOF is three more than this case.