m is optionally substituted for m before ha which itself is followed by m,
The म् may be changed to anusvara or remain unchanged before a word beginning with ह्म ॥ Thus किं or किम् ह्मलयति, 'what does because to shake'? कथं ह्मलयति or कथम् ह्मलयति ॥
Vart:- Before ह्म, ह्व, and ह्ल, the preceding म् may be changed to य, व or ल respectively. Thus किं ह्यः or किय्ँह्यः, 'what does it matter about yesterday'? किं ह्वलयति or किव्ँ ह्वलयति 'what does he cause to shake'? किं ह्लादयति or किल्ँ ह्लादयति 'what gladdens'.,