a = 0
b = 0
c = 0

GOSUB sub

b = 1
c = 1

GOTO trap

END
sub:
    a = 1
    RETURN
    a = 2

trap:
    IF a == 1 AND b == 1 AND c == 1 THEN
        PRINT "success"
    ELSE
        PRINT "fail: ", a, ", ", b, ", ", c
    END IF
    PRINT_FLUSH(message1)
    GOTO trap