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The  \href{http://fretbursts.readthedocs.org/en/latest/ph_sel.html}{\texttt{Ph\_sel}  class} allows to express the expression of  any combination of photon streams. For example, in ALEX measurements, the D-emission during A-excitation stream is  usually excluded because it does not contain any useful signal~\cite{Lee_2005}.  To indicate all but the photons in this photon stream we write