def gen_var(lc, lr):
    """
    Generates the required number of variables. They are defined by the problem.
    
    Args:
    
        lc : number of columns
        lr : number of rows
    
    Returns:
    
        v (list): list with problem variables.
    """
    
    var = lc - lr - 1
    v = []
    
    for i in range(var):
        v.append('x' + str(i+1))
    
    return v