code: public final boolean addConstraintsNoPropagation(Constraint... c) {
  		this.skipPropagation = true;
  		this.addConstraints(c);
  		this.skipPropagation = false;
  		return true;
  	}
docs: Add a batch of constraints between {@link Variable}s, but do not propagate. This method always returns {@code true},
  hence if the constraint(s) to add are inconsistent, this will result in propagation failure the next time
  a constraint is added and propagation occurs.
  @param c The constraints to add.
  @return {@code true}