Will the halogen displace?

A more reactive halogen pushes a less reactive one out of its salt. You will write the test, name what is set free, and list every pair that reacts.

The idea. The order, most reactive first, is F, Cl, Br, I. A free halogen displaces a halide that comes later in the list.

Your tasks.

1. In displaces, return True if the free halogen comes before the halide in order.
2. In freed, return the halogen set free, such as "I2", or "none".
3. Fill pairs with every (halogen, halide) pair from Cl, Br and I that reacts.