When a medial consonant cluster is simplified by deletion or place assimilation, the first consonant is affected, but never the second one: /patka/ becomes [paka] and not *[pata]; /panpa/ becomes [pampa] and not [panta]. This article accounts for that observation within a derivational version of Optimality Theory called Harmonic Serialism. In Harmonic Serialism, the final output is reached by a series of derivational steps that gradually improve harmony. If there is no gradual, harmonically improving path from a given underlying representation to a given surface representation, this mapping is impossible in Harmonic Serialism, even if it would be allowed in classic Optimality Theory. In cluster simplification, deletion or Place assimilation is the second step in a derivation that begins with deleting Place features, and deleting Place features improves harmony only in coda position.
Available at: http://works.bepress.com/john_j_mccarthy/30/