and 
 block here is compiled against a build of the library, run, and
its stated output compared with the one produced, by a harness that reports a page and line
for anything that does not hold. So a sample that names a member the library no longer has
is caught here rather than by a reader.

Two conventions make that work, and both are worth keeping for the reader's sake anyway:

- **using AngouriMath;, using static AngouriMath.MathS; and using static
  AngouriMath.Entity; are implied** in every sample, along with using System;. Anything
  else a sample needs, it states — using System.Numerics; for Complex,
  using AngouriMath.Extensions; for the string extensions.
- **What a sample prints goes in a bare fence introduced by Output:**, on its own line.
  Not 
cs, which marks code. Short outputs may instead be trailing comments on the
  Console.WriteLine lines, and then every printing line needs one.

A block that cannot be a whole program — a fragment, pseudo-code, something written against
a UI, something that throws on purpose — says so in an HTML comment before the fence, which
does not render: