Literature Reference: 至交不可合，一合难离坼。—— 《寄狄拾遗时为魏州从事》 The closest friendship cannot be easily formed, once formed, it is hard to part. Source from 'Ji Di Shiyi Shi Wei Weizhou Congshi'.
至: Arrive; reach the pinnacle, the utmost, attaining the zenith.
交: Handover and intertwine, leaving a favorable impression and excelling in social interactions, fostering good relationships.
Meaning: The closest friendship, deep and unbreakable.