Blurb:

The suicide accounts of three bhikkhus in sutta literature probably inspired
the formulation of a particular type of person who attains Arahantship
at death, later designated as an ‘equal-headed’ (samasīsin) person in the
Abhidhamma. The Theravāda tends to depict those bhikkhus as non-Arahants
before suicide. The Pali commentary explains that they did not attain
Arahantship until their deaths and refers to two of them as each being an
‘equal-header’ (samasīsī). By contrast, the (Mūla-)Sarvāstivāda sūtras and Abhidharma
portray them as Arahants during their lifetimes. The Sarvāstivādins
deny the concept of samasīsin proposed by the Vibhājyavādins, which include
the Theravāda and Dharmaguptaka schools. The Pali commentaries provide
various explanations and classifications of samasīsin, which have one idea in
common: the term signifies the concurrence of two events, and it denotes at
least a person who only becomes an Arahant at death, and sometimes someone
who becomes an Arahant at the same time as a certain kind of event
occurs. The Paṭisambhidāmagga, a quasi-Abhidhamma text, has a chapter that
expounds ‘equal-head’ (samasīsa) in an oblique way by enumerating various
kinds of sama and of sīsa separately. The Paṭisambhidāmagga commentary tries
to make sense of the term samasīsa by associating this textual exposition of
sama and sīsa with the more commonly found term samasīsin.