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Can some please define what ${\displaystyle C}$ is in "Every positive map ${\displaystyle C(X)\to C(Y)}$ is completely positive." Jess_Riedel ( talk) 02:12, 1 April 2020 (UTC) reply

${\displaystyle C(X)}$ is the algebra of complex-valued continuous functions on a compact Hausdorff space ${\displaystyle X}$. This is considered standard notation in C*-algebra theory. Minimalrho ( talk) 14:42, 6 April 2020 (UTC) reply