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We've discussed this before; see

http://www.math.utexas.edu/pipermail/maxima/2003/004869.html

http://www.math.utexas.edu/pipermail/maxima/2003/004870.html

Maybe a simple workaround such as

mysum(f,v,lo,hi):=block([acc:0],

if integerp(lo) and integerp(hi) then for i from lo thru

hi do acc:acc+substitute(i,v,f)

else acc:funmake('mysum,[f,v,lo,hi]),

acc)

or

mysum(f,lo,hi):= block([acc:0],

if integerp(lo) and integerp(hi) then

for i : lo thru hi do acc : acc + apply(f,[i])

else acc : funmake('mysum,[f,lo,hi]),

acc);

might work for you,

Barton