Update docs and example materials.

doc/en/STACK_question_admin/Sample_questions.md

@@ -24,6 +24,8 @@ This directory contains sub-directories with large libraries of questions:
 
 We would encourage colleagues to release their materials under a creative commons licence.  Please contact the developers.
 
+A significant advantage of using questions from the STACK library is that they are distributed with the source code, and therefore use features which match your version of STACK.
+
 # Moodle courses released with STACK #
 
 STACK is released with a demonstration course which contains hundreds of tested STACK questions.  Many have a full worked solution and random variants, and this represents a substantial resource.

doc/en/Topics/Proof/index.md

@@ -8,6 +8,7 @@ A discussion of [_Practical Online Assessment of Mathematical Proof_](https://ww
 
 * faded worked examples,
 * reading comprehension questions.
+* Fill in the blanks.  E.g. in the question library see `Topics/LinearAlgebra/Diagonalizable-proof-comprehension.xml`.
 
 Such questions can be written in STACK.  In addition 
 
@@ -25,7 +26,7 @@ Mathematical writing, especially for students, commonly takes two forms.
 1. A mathematical proof, which is a deductive justification of a claim.  A proof is a "checkable record of reasoning".
 2. A mathematical recipe, which is a set of instructions for carrying out a procedure.
 
-## Presentation of proof
+## Presentation of proof in STACK
 
 STACK supports representation and display of mathematical proof as trees, with string nodes for the individual sentences/clauses in the proof.  The goals of representing proofs as trees of text-based strings are as follows.
 

doc/en/Topics/index.md

@@ -2,8 +2,6 @@
 
 This section of the STACK documentation contains information on how to author questions in particular mathematical topics.  Many topics have different requirements, e.g. physics needs support for scientific units.  These pages contain know-how on linking together features such as [inputs](../Authoring/Inputs/index.md), [answer tests](../Authoring/Answer_Tests/index.md) and [options](../Authoring/Question_options.md) to write questions in particular subject areas.
 
-Current topics include:
-
 * [Curve sketching](Curve_sketching.md)
 * [Differential equations](Differential_equations.md)
 * [Discrete mathematics](Discrete_mathematics.md)
@@ -15,3 +13,5 @@ Current topics include:
 * [Proof](../Topics/Proof/index.md).
 
 There is separate documentation on [specialist tools](../Specialist_tools/index.md), such as those needed for, drag and drop (Parsons problems), graphical interaction and so on.  Specialist tool documentaion is not linked to a single mathematical topic, but rather to a technical tool.
+
+The stack question library contains many examples in directories matching the structure of the documentation.

samplequestions/stacklibrary/Topics/LinearAlgebra/Eigenvalues-eigenvectors-give-examples.xml

@@ -7,19 +7,15 @@
     </name>
     <questiontext format="html">
       <text><![CDATA[<p>A \(2\times2\) matrix \(A\) has eigenvalues \(\lambda_1 = 1\), \(\lambda_2 = {@a2@}\).</p>
-
-<ol class="HELM_parts">
-
+<ol>
     <li>
         <p>Find the characteristic polynomial of \(A\).</p>
         <p>\(c_A(x)=\) [[input:ans1]] [[validation:ans1]] [[feedback:prt1]]</p>
     </li>
-
     <li>
         <p>Give an example of matrix \(A\).</p>
         <p>[[input:ans2]] [[validation:ans2]] [[feedback:prt2]]</p>
     </li>
-
     <li>
         <p>Find the eigenvectors of \(A\) in part (b).</p>
         <div style="padding: 0.5em">
@@ -42,9 +38,8 @@
 </ol>]]></text>
     </questiontext>
     <generalfeedback format="html">
-      <text><![CDATA[<p dir="ltr" style="text-align: left;"></p>
-<h4>Worked Solution</h4>
-  <ol class="HELM_parts">
+      <text><![CDATA[<h4>Worked Solution</h4>
+  <ol>
   <li><p> The theorem of characteristic polynomial: If \(A\) is an \(n\times n\) matrix, a number \(\lambda\) is an eigenvalue of \(A\) if and only if \(c_A(\lambda) = 0\), that is if and only if \(\lambda\) is a root of the characteristic polynomial \(c_A(x)\).
 In this question, we have eigenvalues \(\lambda_1 = 1\) and \(\lambda_2 = {@a2@}\). By the theorem, the characteristic polynomial is \((x-1)(x-{@a2@})\).</p></li>