Double check also be possible. For example, in the position shown, after Black plays 1...d5, White plays 2.exd6e.p. quintuple check (the "moa" is a non-leaping knight which first takes a diagonal step, then an orthogonal one). After the "en passant" capture, five pieces check the black king: both moas, the rook, the grasshopper and the bishop. In xiangqi, the Chinese version of chess, triple check and even quadruple check is possible even without using fairy pieces, as in the following examples: Double check In chess, a double check is a check delivered by two pieces simultaneously. In chess notation, it is almost
Quadruple product Quadruple product In mathematics, the quadruple product is a product of four vectors in three-dimensional Euclidean space. The name "quadruple product" is used for two different products, the scalar-valued scalar quadruple product and the vector-valued vector quadruple product or vector product of four vectors . The scalar quadruple product is defined as the dot product of two cross products: where a, b, c, d are vectors in three-dimensional Euclidean space. It can be evaluated using the identity: or using the determinant: The vector quadruple product is defined as the cross product of two cross products: where a, b, c, d