Transmission and complete operational input

For universal qubit cloning there is also a direct affine proof: the two decompositions of $I/2$ into the $Z$ and $X$ basis ensembles would give different two-copy outputs. Landmark I uses that universal-input argument CheungI (thm:nocloning). The fidelity argument additionally explains why a physical deterministic map cannot exactly clone even a specified pair of nonorthogonal pure states WoottersZurek,Dieks.