For integers a,b and positive M, a is congruent to b modulo M when M divides a-b. The least nonnegative residue is the unique integer r with 0<=r<M and a-r divisible by M. A system on n declared Boolean variables has a count N between 0 and 2^n. Set ell=n+1. If an integer Z is congruent to N modulo 2^ell, its least nonnegative residue is N itself, because 2^n<2^ell. A modulus of 2^n would fail: counts zero and 2^n have the same residue. Variables unused by any equation still count as declared variables and double the number of assignments.