import random


def mutation_set(num_indiv, num_genes, num_mut=0):
    """
    Prepares a list of genes to be mutated for the function `mutate_population`.
    
    Parameters
    ----------
    num_indiv : int
      Number of individuals.
    num_genes : int
      Number of genes.
    num_mut : int
      Number of mutations.
      
    Returns
    -------
    List of lists of int
      List of lists of genes positions to be mutated.
    """
    
    if num_genes <= 1:
        return 0
    
    mutated_genes = []
    for i in range(num_indiv):
        tmp_set = [random.randint(0, num_genes-1), random.randint(0, num_genes-1)]
        while tmp_set[0] == tmp_set[1]:
            tmp_set[1] = random.randint(0, num_genes-1)
        mutated_genes.append(tmp_set)

    print(mutated_genes)
    return mutated_genes