1.2 (BOI'95) Expression

                   Evaluation protocol

         Input                                Output          Points
----------------------------------------------------------------------
test 1   765                                  765              2p

test 2   40+a-d        a=-38, d=100           -98              3p

test 3   250ea-50c+4   a=-1, e=-2, c=5        254              3p

test 4   -10babc+12aa  a=2, b=2, c=1          -32              3p

test 5   25abc                                UNDEFINED        2p

test 6   123acb+14de   a=2, b=12, d=-120      UNDEFINED        2p

test 7   ab+abcd+98    a=2, b=0, d=3          98               5p

test 8   59ac-bc-52c+431a   b=7, a=1          431              6p

test 9   a-cb+def-gh
         a=7, h=1, g=11, c=3, b=-1,
         d=4, e=5, f=10                       199              2p
test 10  -a+b-a+b-a+b-a+b-a+b-a+b-a+b-a+b-
         a+b-a+b
         a=-200000000
         b=-199999999                         10               2p

                                                            -----------
                                                       Total   30p


        The points for UNDEFINED are assigned only when at least
one positive test containing variables is correct.