Usem is located in:
unix/src/solaris-2-x/Usem.i3
unix/src/ultrix-3-1.generic/Usem.i3
unix/src/ibm-4-3/Usem.i3
unix/src/sysv-4.0/Usem.i3
unix/src/hpux-7-0/Usem.i3
unix/src/sunos-4-x/Usem.i3
unix/src/freebsd-1/Usem.i3
unix/src/linux/Usem.i3
unix/src/aix-ps2-1-2/Usem.i3
unix/src/freebsd-2/Usem.i3
unix/src/irix-5.2/Usem.i3
unix/src/osf-1.generic/Usem.i3
unix/src/aix-3-2/Usem.i3