Assertion: bullet train | /r/HasProperty | undergone upgrade
Facets:
value: since their implementation
type: TEMPORAL
Source sentences:
text: Originally proposed in the early 1940s, the first bullet trains were not opened until the mid-1960s, and have undergone many improvements and upgrades since their implementation.
text: Originally proposed in the early 1940s, the first bullet trains were not opened until the mid-1960s, and have undergone many improvements and upgrades since their implementation.