Which metal displaces which?

Six metals are listed in the order of the reactivity series, the most reactive first. You will write a function that says whether one metal displaces another from its salt, count how many each metal displaces, and find the metals that displace none.

The idea. A metal displaces another from its salt solution only if it is higher in the series, which here means earlier in the list.

Your tasks.

1. In displaces, return True when metal comes before other in series.
2. Fill table with how many of the other metals each metal displaces.
3. Find never, the list of metals that displace none of the others.