/**
 * Least squares via Householder QR: min ||Ax - b||_2.
 *
 * Works directly on A (n x p, n >= p) instead of the normal equations, so the
 * condition number is not squared — near-collinear designs stay solvable.
 * Returns false when A is (numerically) rank deficient or n < p; callers
 * should surface an informative error rather than produce garbage.
 */
export declare function lstsq(A: number[][], b: number[]): number[] | false;