private static boolean contains(int[] list, int key) {
        for (int candidate : list) {
            if (candidate == key) return true;
        }
        return false;
    }
Creates a reduce function.

@param argument the tensor to reduce
@param aggregator the aggregator function to use
@param dimensions the list of dimensions to remove. If an empty list is given, all dimensions are reduced,
                  producing a dimensionless tensor (a scalar).
@throws IllegalArgumentException if any of the tensor dimensions are not present in the input tensor
vespajlib/src/main/java/com/yahoo/tensor/functions/Reduce.java