The three-element linear concatenative basis
Brent Kerby calls out that ‘take’, ‘cat’, and ‘i’ are a linear basis in a concatenative language.
[B] [A] take == [A [B]] [B] [A] cat == [B A] [A] i == A
This is a valid basis because ‘take’ covers quoting, concatenation, and reording; ‘cat’ covers concatenation; and ‘i’ covers unquoting. (Note that concatenation is covered twice, which is why there is a possible two-instruction basis.)