一而二，二而一 [－－－－－－－]

Jyutping jat1 ji4 ji6 ， ji6 ji4 jat1
Pinyin yī ér èr ， èr ér yī

Definitions (Wiktionary)
  1. phrase, idiomatic
    two sides of the same coin
  2. phrase, idiomatic
    one and the same