Here a Boolean-indexed tensor is a function T that takes an ordered list of d bits and returns one number or ring element. The d input positions are called ports. For d=2, the entries T(0,0), T(0,1), T(1,0), T(1,1) form a two-by-two table. Boolean describes the indices, not the values: entries can be integers or truncated polynomials. For d=0, the tensor has one scalar entry. A tensor can be described by a procedure that computes a requested entry rather than by explicitly storing all 2^d entries.