UNDEF refform_old 703 703 705 
unary_+: numbers 538 538 541 
unary_-: numbers 539 539 541 
undef refform 818 818 820 
undef words 308 308 312 
undef_key ident 671 671 673 
undefword ident 648 648 650 
unftrace metaflavour_flavour 155 155 159 
unftrace metaflavour_flavour 156 156 159 
unftraceall metaflavour_flavour 162 162 165 
unless syntax 788 788 793 
unpackitem data 401 401 406 
until syntax 796 796 801 
untrace trace 42 42 45 
untraceall trace 48 48 50 
updater procedure 167 168 171 
updaterof syntax 804 804 805 
updating_last syntax 808 808 810 
uppertolower strings 454 454 461 
uses library 563 563 568 
uses_lib_idents library 571 571 572 
useslib library 575 575 579 
using_subscriptor syntax 813 813 819 
uts mishap_codes 428 429 436