Just taking an advance in what I want to learn someday: I understand that decoherence and entanglement are more or less equivalent. So, I take it decoherence is in principle a process of entanglement. Consider two particles A and B who are entangled. if A decoheres by interacting with particle C, are then B and C entangled with each other? And if C dehoheres futher by interacting with particle D, are then B and D entangled, and so forth? If so, suppose D decoheres all the way to the top: particle X, and X is, in some magical way, the readout of the measuring device on the one side. Similarly B decoheres to particle (and readout) Y. Does this mean that if I manipulate some property of particle X, it will have consequences for the equivalent property of particle Y? That is to say, do we have instant correlation between X and Y? I guess we have to restrict ourselves to a linear chain of particles on both sides, so not diverging into a macroscopic reaout. What I mean is: if we have a chain of entanglement, does manipulating one end put restrictions on the outcomes of the other end in order to keep the value of the correlation constant? I hope the question is clear.