+ <sect1 id="command_unification_hint">
+ <title>unification hint</title>
+ <para><userinput>unification hint n ≔ v1 : T1,… vi : Ti; h1 ≟ t1, … hn ≟ tn ⊢ tl ≡ tr.</userinput></para>
+ <para>
+ <variablelist>
+ <varlistentry>
+ <term>Synopsis:</term>
+ <listitem>
+ <para>
+ <emphasis role="bold">unification hint</emphasis>
+ &nat;
+ <emphasis role="bold">≔</emphasis>
+ [ &id; [ <emphasis role="bold">:</emphasis> &term; ] ,.. ]
+ <emphasis role="bold">;</emphasis>
+ [ &id; <emphasis role="bold">≟</emphasis> &term; ,.. ]
+ <emphasis role="bold">⊢</emphasis>
+ &term; <emphasis role="bold">≡</emphasis> &term;
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>Action:</term>
+ <listitem>
+ <para>Declares the hint at precedence <command>n</command></para>
+ <para>The file <command>hints_declaration.ma</command> must be
+ included to declare hints with that syntax.</para>
+ <para>Unification hints are described in the paper
+ "Hints in unification" by
+ Asperti, Ricciotti, Sacerdoti and Tassi.
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </para>
+ -->
+ </sect1>
+ <sect1 id="command_universe_constraints">
+ <title>universe constraint</title>
+ <para>TODO</para>
+ <!--
+ <para><userinput>coercion u with ariety saturation nocomposites</userinput></para>
+ <para>
+ <variablelist>
+ <varlistentry>
+ <term>Synopsis:</term>
+ <listitem>
+ <para>
+ <emphasis role="bold">coercion</emphasis>
+ (&uri; | &term; <emphasis role="bold">with</emphasis>)
+ [ &nat; [&nat;]]
+ [ <emphasis role="bold">nocomposites</emphasis> ]
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>Action:</term>
+ <listitem>
+ <para>Declares <command>u</command> as an implicit coercion.
+ If the type of <command>u</command> is
+ <command>∀x1:T1. … ∀x(n-1):T(n-1).Tn</command> the coercion target is
+ <command>T(n - ariety)</command> while its source is
+ <command>T(n - ariety - saturation - 1)</command>.
+ Every time a term <command>x</command>
+ of type source is used with expected type target, Matita
+ automatically replaces <command>x</command> with
+ <command>(u ? … ? x ? … ?)</command> to avoid a typing error.</para>
+ Note that the number of <command>?</command> added after
+ <command>x</command> is saturation.
+ <para>Implicit coercions are not displayed to the user:
+ <command>(u ? … ? x)</command> is rendered simply
+ as <command>x</command>.</para>
+ <para>When a coercion <command>u</command> is declared
+ from source <command>s</command> to target <command>t</command>
+ and there is already a coercion <command>u'</command> of
+ target <command>s</command> or source <command>t</command>,
+ a composite implicit coercion is automatically computed
+ by Matita unless <emphasis role="bold">nocomposites</emphasis>
+ is specified.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </para>
+ -->
+ </sect1>