[en] A weak two-proton azimuthal angle back-to-back correlation which may indicate the presence of quasi-elastic first order proton-proton scattering in ¹⁶O + CNO reactions at 2 GeV/nucleon has been observed. Low and medium multiplicity ¹⁶O + AgBr reactions show the same tendency, while the dominant feature of the two-proton azimuthal angle distribution for very high multiplicity events is a blockade against pairs with relative angles between 2π/3 and 7π/8. (Auth.)