The rocket pattern in slitherlink is when a 3 sees a 1 in a diagonal, with two crosses (the exhaust) on the opposite side.
3 x 1 x
two lines can be added adjacent to the 3 and opposite to the 1, making the top of the rocket.
_ 3| x 1 x
I used the reverse pattern several times, but I cannot prove that it is true or just a coincidence.
_ _ 3| 3| 1 ====> x 1 x
Is there a proof that the "reverse rocket" is a valid pattern?