semiprojection noun1 •A function f of rank k, where k is greater than or equal to three, such that for some index i between one and k (inclusive), f(x₁, x₂, ... xₖ) = xᵢ whenever |{x₁, x₂, ... xₖ}| < k.We now show that closure under a semiprojection operation is not in general a sufficient condition for tractability. — 1997 formssemiprojections
