In Norman's translation of the Dhammapada, in his note for v.259, he directs the reader's attention to verses 8, 128, 168, 172 and 177, where there is the same consonant doubling of p before na as in v.259 (pamajjati to nappamajjati) after what he calls the 'proclitic' use of na. So the formation seems to be a regular phonological feature in Pali.
Dhivan
www.dhivan.net
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