Conditional
if then else

The process if B then P else Q  behaves as the process P if the condition B is true otherwise it behaves as Q. If the else Q is omitted and B is false, then the process behaves as STOP.

Re-labeling /

Re-labeling is applied to a process to change the names of action labels. The general form of re-labeling is:
/{newlabel_1/oldlabel_1,… newlabel_n/oldlabel_n}.

Hiding \

When applied to a process P, the hiding operator \{a1..ax} removes the action names a1..ax from the alphabet of P and makes these concealed actions "silent". These silent actions are labeled tau.  Silent actions in different processes are not shared.

Interface @

When applied to a process P, the interface operator @{a1..ax} hides all actions in the alphabet of P not labeled in the set a1..ax.