An error while making Open inventor

[vmirinav@netscape.net (Vito Mirinavicius)]

I get the following error while compiling Open Inventor under 
Redhat 7.3 
the compiliation works fine if I get rid of the [-lXm]. 
Is that legal to do? What package do you think I am missing?  

/usr/bin/g++   -L///usr/lib/InventorDebug  -shared -Wl,--whole-archive    -L/usr/X11R6/lib libInventorXt.a  -lXm -lXt -lXext -lXi -lX11 -lm -lInventor -lGLU -lGL -lXp  -Wl,--no-whole-archive -o libInventorXt.so
/usr/bin/ld: cannot find -lXm
collect2: ld returned 1 exit status
make[1]: *** [libInventorXt.so] Error 1
make[1]: Leaving directory `/home/user/vito/inventor/libSoXt'
make: *** [all] Error 1

Thank you in advance 

Vito

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