momkai lujvo

x1 is the x2-th member of set x3 ordered by rule x4

In notes:

momvelru'e
x1 is the x2-th stage in process x3.
pormoi
x1 is in the x2-th slot of sequence x3
etmoi
x1 is the value (sumti-object) associated with x2 (label or description), from compound object x3, in interpretation rules/system x4