private Long getVerticeInKWithPositiveDegreeUsingOnlyEdgesFrom(
			List<Long> k, Set<Long> usableEdges) {
		for (Long e : k) {
			for (Long v : graph.getSourceTarget(e)) {
				countAccess(1); 
				if (degreeWithinEdges(v, usableEdges) > 0) {
					return v;
				}
			}

		}
		return NULL_IDX;
	}