The past is once upon a time
Once upon a time is past
The past is yesterday today

from Madvillain (Ft. Madlib & Quasimoto) – Shadows of Tomorrow Lyrics on Rap Genius

Meaning

Connecting it all together. The past has many names but it is still time stretching backward from the present.
(To me it sounds like the “today” at the end of the line is just echo from him saying yesterday.)

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