An indicator function converts a condition into a deterministic value: it returns 1 when the condition holds and 0 otherwise. In a structural causal model, it can assign an outcome using a uniform exogenous variable. section 6.2.1
Coin-flip assignment
Sample u from Uniform(0, 1), then set y := I(u ≤ pₓ). If u falls below the selected coin’s probability pₓ, y is 1; otherwise, y is 0. Repeating this procedure produces Bernoulli samples. section 6.2.1
This reparameterization moves randomness into an exogenous variable and leaves the indicator as the assignment function; alternative reparameterizations can encode different causal assumptions. section 6.2.1

