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Dear Tarcer creators,

despite the fact that I never found Tarcer doing anything wrong I frequently came across 'strange' beahviour. Mostly it boiled down to a lack of proper understanding on my side, but one class of cases remained:

(1) TJI[d, m1^2 ,{{3,m2},{1,m2},{1,m1}}]

(2) TJI[d, m1^2 ,{{2,m2},{2,m2},{1,m1}}]

(1) TJI[d, m1^2 ,{{2,m2},{2,m1},{1,m2}}]

are not recursed down to basis integrals. The recursion formulas (74) and (81) in hep-ph/9801383 boil down to 0 = 0 for certain kinematical configuarations. In this case one has to go off-shell (m1^2 -> s) and then divide out a zero, such that a nontrivial recursion relation remains. the coefficients of the ladder operators then have single or double zeros of the form (s-m1^2)^(1 or 2).

I could solve the last case in a straightforward fashion and the first two by deriving a simplified relation from (81) which led from (1) to (2) and back. In this way I got a 2x2 system in (1) and (2).

Tarcer.nb is too advanced to allow me to provide a patch (in case one is needed, probably I have just not yet seen how to do the recursion using TarcerRecurse) so i though i'd let you know.

best regards

robert schoefbeck

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