Def Unit == 0  

is mentioned by

Def trigger1(loc;T;A;P;i;k;a;x) Def == [(recognizer1(loc;T;A;P;k;i;"trigger";x));  Def == [if loc = i ma-single-pre1("trigger";;a;Unit;x,v.x) else  fi]	[trigger1]
Def send-once(loc;T;A;a;f;tg;l;x) Def == [(once(loc;a;source(l)));  Def == [if loc = source(l) Def == [if ma-single-sends1(A; Unit; T; x; locl(a); l; tg; (a,b. [(f(a))])) Def == [else  fi]	[send-once]
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	[once]

In prior sections: core mb event system 6 bool 1 mb event system 3

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