Repeated event with cut-set absorption
A shared basic event feeds two gates — the case naive fault-tree tools get wrong. MOCUS applies absorption so the supersets collapse, leaving two single points of failure that a shape stencil would miss.
For the safety analyst who needs the math right
What this shows
MSF feeds both G1 and G2 — a repeated event, the DAG case that separates a real engine from a shape stencil. It is drawn once per reference with the shared-event mark, but the cut-set engine treats every instance as the same Boolean variable.
Absorption is the point. MOCUS first expands the tree to {MSF, ESF}, {MSF, RCF}, {MSF}, {CDM}. Because {MSF} is itself a cut set (via G2), the larger sets {MSF, ESF} and {MSF, RCF} are absorbed — a superset of a cut set is not minimal. The two minimal cut sets are {MSF} and {CDM}, both order-1 single points of failure (boxed in the strongest red). A naive expander that forgets absorption would wrongly report four. P(top) ≈ P(MSF) + P(CDM) = 0.0044.