Function do_intervene 

pub fn do_intervene(
    edges: &[NQuin],
    roots: &[u64],
    set_present: &[u64],
    set_absent: &[u64],
    effect: u64,
) -> bool

Intervention do(...): force the variables in set_present to occur and set_absent to NOT occur — severing the absent nodes from the graph and treating the present ones as exogenous roots — then compute whether effect results (P(effect | do(X)) as boolean reachability). Zero-heap.