x1 is a logical 'if-else' (ternary conditional) statement saying that if x2 is true, then x3 is true (or performed), but otherwise/else (if x2 is not true, then) x4 is true (or performed).
x1 is a material conditional/'IF' statement (logical statement) saying that x2 (du'u) logically implies x3 (du'u) ("x3 is true if x2 is true; if x2, then x3; x2 being true is sufficient to guarantee the truth of x3").