In a sentence like:
我很高兴 (wǒ hěn gāoxìng)
two 3rd tones are in a row. So according to 3rd tone sandhi, it must be pronounced
wó hěn gāoxìng
On the other hand, a 3rd tone (hěn) is followed by a non 3rd tone, so it must be pronounced half 3rd tone. By putting these two rules together we get:
wó hěn(half-3rd) gāoxìng
Is this method of combing two tone rules correct?