x1 is the whole region of space which is between inner sphere x2 and outer sphere x3.
x1 canlu. The two spheres need not be mutually concentric, but x3 should enclose at least some portion (and probably: most) of x2 and, without loss of generality, x3 should be radially larger than or congruent to x2; if x2 is not fully enclosed by x3, then the result is the convex hull formed by them or some smoothed version or inflation thereof, minus every point enclosed by x2 (and possibly minus x2 itself). Containment, by x1, of any points belonging to the (surfaces) of x2 or x3 is left vague and may be specified by additional description. Contrast with "jinrcaibyca'u", which a thin toroidal region enclosed by a bolbi'i (under the assumption of nesting: x2 being wholly enclosed by x3) and confined approximately to a plane intersecting therewith (and which nearly requires complete enclosure of x2 by x3). Just use "jbini" with a path or interval defined by the centers or mutually-nearest surface points of x2 and x3 if x2 is not at least partially enclosed by x3. Use "neryrelbolbi'i" if you want to be extremely clear in meaning.