subset<T> function
Set operations
Returns true if a is a subset of b: if every value in the given
iterable a is also in the given iterable b.
subset([1, 3], [0, 2, 1, 3, 0]); // true
Implementation
bool subset<T>(Iterable<Object?> a, Iterable<Object?> b) {
return superset(b, a);
}