** ELT signals an error of type TYPE-ERROR when the index argument
is not a valid sequence index;
** LOOP signals (at macroexpansion time) an error of type
PROGRAM-ERROR when duplicate variable names are found;
** ELT signals an error of type TYPE-ERROR when the index argument
is not a valid sequence index;
** LOOP signals (at macroexpansion time) an error of type
PROGRAM-ERROR when duplicate variable names are found;