For ten points, identify this property held by two members of a space if their inner product is zero.
Jessen's [this] icosahedron is a shaky polyhedron in which faces of an icosa- hedron are replaced by isosceles triangles. Polynomials are described using this term if they obey the relationship that the integral from a to b of w(x)pm(x)pn(x) is equal to cn times the Kronecker delta of m and n. Circles in the plane are the group orbits of groups described by this term, of which the special kind is the component containing the identity. This condition for linear transformations can be expressed as aijaik is equal to the Kronecker delta of j and k. Three confocal conic   surfaces have this property, which can be attained by at most three collections of surfaces in three-dimensional space. For ten points, identify this property held by two members of a space if their inner product is zero.
Jessen's [this] icosahedron is a shaky polyhedron in which faces of an icosa- hedron are replaced by isosceles triangles.
orthogonality [accept word forms, prompt on perpendicularity and word forms]