32. ithu a enRum u enRum ma enRum mUnRu thiruvaksharam.
This praNavam is the combination of the three aksharas "a", "u" and "m".
Sri PBA Swami's Sarartha Deepikai:
Here the aksharas that make up the praNava are being shown separately. The akAram (a) and ukAram (u) combine by grammatical rules to form the "O" and therefore the praNavam is made up of a, u and m.
The sruti shown before says "Omiti EkAksharam", meaning that the praNavam is just one akshara. So, how can we say that it is made up of three aksharas?
There are two rules to consider. One is called samhitAkAram and the other is asamhitAkAram. The AkAram that is formed using the combination rules (sandi) is called samhitAkAram; the AkAram that is not formed using the combination rules is called asamhitAkAram. Using asamhitAkAram (non-combination), the praNavam is made up of three parts (each letter is a part) and gives three meanings. When samhitAkAram (combination) is used, the praNavam is one letter making one part and has one meaning. Thus the sruti "OmityEkAksharam" is based on samhitAkAram.