¶The three-element linear concatenative basis
Brent Kerby calls out that take, cat, and i are a linear basis in a concatenative language.
The Theory of Concatenative Combinators » Linear Completeness
[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.)
Categories of instructions in a concatenative basis