@Override
    public boolean equals(Object obj) {
        if (obj == this) {
            return true;
        }
        if (!(obj instanceof FeatureConjunction)) {
            return false;
        }
        FeatureConjunction rhs = (FeatureConjunction)obj;
        if (!operands.equals(rhs.operands)) {
            return false;
        }
        return true;
    }
A FeatureConjunction is a special type of Conjunction where
all children are either a FeatureSet or a Negation (with an underlying FeatureSet).
The underlying FeatureSets may only have one value.

@author bjorncs
predicate-search-core/src/main/java/com/yahoo/document/predicate/FeatureConjunction.java