When do do:

?NOLIST, SOURCE =util(term_write_int)

You are telling the TAL compiler to look for a TACL DEFINE called "=UTIL". If you want to do it in this way, you should add the DEFINE to TACL environment before calling the TAL compiler for compiling your main, otherwise you will receive that error "No file system DEFINE exists for this logical file name: =util"

you can reference your file directly:

?NOLIST, SOURCE $vol.subvol.util(term_write_int)

Or, previously calling the compiler:

ADD DEFINE =UTIL, FILE $VOL.SUBVOL.UTIL

TAL /IN MAIN/ ....