  This write up attempts to clarify a preprint by Markarian [2] which proves
This paper attempts to clarify a preprint of Markarian [2]. The preprint by
Markarian [2] proves the relative Riemann-Roch theorem using a result
describing how the HKR map fails to respect comultiplication. This paper
elaborates on the core computations in [2]. These computations show that the
HKR map twisted by the square root of the Todd genus "almost preserves" the
Mukai pairing. This settles a part of a conjecture of Caldararu[3]. The
relative Riemann-Roch theorem follows from this and a result of Caldararu[4].
