docs: @Pure
  	@Inline(value = "$3.union($1, $4.singletonMap($2.getKey(), $2.getValue()))",
  			imported = { MapExtensions.class, Collections.class })
  	public static <K, V> Map<K, V> operator_plus(Map<K, V> left, final Pair<? extends K, ? extends V> right) {
  		return union(left, Collections.singletonMap(right.getKey(), right.getValue()));
  	}