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The hint that the result is correct if cos(x) is declared

zero is key.

It seems the problem is in sin-cos-intsubs1 in defint.lisp.

There's a clause there:

\(\(not \(equal \($asksign denom\) '$zero\)\) 0.\)

This seems bizarre. If the denom is not zero, why should it

return 0? My limited understanding is that sin-cos-intsubs1

is supposed to substitute the limits of the integral into

the indefinite integral. (Which, by the way is correctly

computed by antideriv.)

Changing it to read (equal ($asksign denom) '$zero)) makes

more sense, but I don't know about returning zero as the

result. Undefined or infinity seems better, if a choice

must be made.