// Toy model of a 4 states cycle
Node C
{
rate_up=0.0;
rate_down=((NOT A) AND (NOT B)) ? $escape : 0.0 ;
}

Node A 
{
rate_up=(C AND (NOT B))  ? $Au : 0.0;
rate_down= B ? $Ad : 0.0;
}

Node B 
{
rate_up= A ? $Au : 0.0;
rate_down = A ? 0.0 : $Ad ;
}