def check_operation_once(matrix):
    """    
    Check if the solution violates the operation once constraint.
    Returns True if the constraint is violated.       
    
    Keyword arguments:
    matrix (List[List[int]]): Matrix of x_i,t values
    """
    for x_it_vals in matrix:
        if sum(x_it_vals) != 1:
            return True
    return False