Def once(loc;a;i)
Def == if loc = i
Def == if [ma-single-pre-init1("done";;false;a;Unit;x,v.x); 
Def == if [only members of [locl(a)] affect "done" :; 
Def == if [ma-single-effect0("done";;locl(a);Unit;x,v. true)]
Def == else nil fi

is mentioned

In prior sections: mb event system 7

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