efn

    OpenVMS usage:ef_number
    type:         longword (unsigned)
    access:       read only
    mechanism:    by value
    Number of any event flag in the common cluster to be
    disassociated. The efn argument is a longword containing this
    number; however, $DACEFC uses only the low-order byte. The number
    must be in the range of 64 through 95 for cluster 2, and 96
    through 127 for cluster 3.