EVQAT PDX     0,4
       TXL     EVQNF,4,0          EXIT IF END OF ATOM
       CLA     0,4                NEXT WORD
       PAX     0,4                CAR OF ATOM
       STL     EVQST              SET SWITCH FOR SUBR OF EXPR
       TXL     *+2,4,$SUBR-1      LOOK FOR $SUBR
       TXL     EVQFS,4,$SUBR      TREAT AS FSUBR (ALMOST)
       TXL     *+2,4,$EXPR-1      LOOK FOR $EXPR
       TXL     EVQFX,4,$EXPR      TREAT AS FEXPR (ALMOST)
       STZ     EVQST              SET SWITCH FOR FSUBR OR FEXPR
       TXL     *+2,4,$FSUBR-1     LOOK FOR FSUBR
       TXL     EVQFS,4,$FSUBR
       TXL     EVQAT,4,$FEXPR-1   LOOK FOR FEXPR
       TXH     EVQAT,4,$FEXPR
 EVQFX PDX     0,4                FOUND AN FEXPR