def METHOD_NAME(gate_indices, number_of_qubits):
    """Return the index string for Numpy.einsum matrix-matrix multiplication.
    The returned indices are to perform a matrix multiplication A.B where
    the matrix A is an M-qubit matrix, matrix B is an N-qubit matrix, and
    M <= N, and identity matrices are implied on the subsystems where A has no
    support on B.
    Args:
        gate_indices (list[int]): the indices of the right matrix subsystems
                                   to contract with the left matrix.
        number_of_qubits (int): the total number of qubits for the right matrix.
    Returns:
        str: An indices string for the Numpy.einsum function.
    """
    mat_l, mat_r, tens_lin, tens_lout = _einsum_matmul_index_helper(gate_indices, number_of_qubits)
    # Right indices for the N-qubit input and output tensor
    tens_r = ascii_uppercase[:number_of_qubits]
    # Combine indices into matrix multiplication string format
    # for numpy.einsum function
    return "{mat_l}{mat_r}, ".format(
        mat_l=mat_l, mat_r=mat_r
    ) + "{tens_lin}{tens_r}->{tens_lout}{tens_r}".format(
        tens_lin=tens_lin, tens_lout=tens_lout, tens_r=tens_r
    )