173. One or two exceptions

There are one or two exceptions to these rules:

a. If the initial sibilant has a surd mute after it, the final s may be dropped altogether—and by some authorities is required to be so dropped. Thus, vāyava stha or vāyavaḥ stha; catustanām or catuḥstanām. With regard to this point the usage of the different manuscripts and editions is greatly at variance.

b. Before ts, the s is allowed to become visarga, instead of being retained.