Consistently use `set_` prefix.

```
sed 's/collection\_equiv/set\_equiv/g;
s/set\_equivalence/set\_equiv\_equivalence/g;
s/collection\_subseteq/set\_subseteq/g;
s/collection\_disjoint/set\_disjoint/g;
s/collection\_fold/set\_fold/g;
s/collection\_map/set\_map/g;
s/collection\_size/set\_size/g;
s/collection\_filter/set\_filter/g;
s/collection\_guard/set\_guard/g;
s/collection\_choose/set\_choose/g;
s/collection\_ind/set\_ind/g;
s/collection\_wf/set\_wf/g;
s/map\_to\_collection/map\_to\_set/g;
s/map\_of\_collection/map\_of\_set/g;
s/\bof\_list/set\_of\_list/g;
s/\bof\_option/set\_of\_option/g;
s/elem\_of\_of\_list/elem\_of\_set\_of\_list/g;
s/elem\_of\_of\_option/elem\_of\_set\_of\_option/g;
s/collection\_not\_subset\_inv/set\_not\_subset\_inv/g;
' -i $(find -name "*.v")
```