From 2b475a8695f1a36b14d16e38fbe38a5bbfc7050c Mon Sep 17 00:00:00 2001
From: Joe Edwards <80713360+Joseph-Edwards@users.noreply.github.com>
Date: Sat, 31 Aug 2024 12:31:48 +0100
Subject: [PATCH] Add new function `MeetBlist` (#5778)

---
 doc/ref/blist.xml                  |  1 +
 lib/list.g                         | 29 +++++++++++++++++++++++++++++
 tst/testinstall/kernel/blister.tst | 10 +++++-----
 3 files changed, 35 insertions(+), 5 deletions(-)

diff --git a/doc/ref/blist.xml b/doc/ref/blist.xml
index 79f780b687..f0e0210455 100644
--- a/doc/ref/blist.xml
+++ b/doc/ref/blist.xml
@@ -56,6 +56,7 @@ In function names we call boolean lists <E>blists</E> for brevity.
 <#Include Label="UniteBlistList">
 <#Include Label="IntersectBlist">
 <#Include Label="SubtractBlist">
+<#Include Label="MeetBlist">
 <#Include Label="FlipBlist">
 <#Include Label="SetAllBlist">
 <#Include Label="ClearAllBlist">
diff --git a/lib/list.g b/lib/list.g
index 33866ac617..e132b2ac6f 100644
--- a/lib/list.g
+++ b/lib/list.g
@@ -881,6 +881,35 @@ DeclareSynonym( "IntersectBlist", INTER_BLIST );
 ##
 DeclareSynonym( "SubtractBlist", SUBTR_BLIST );
 
+#############################################################################
+##
+#F  MeetBlist( <blist1>, <blist2> )
+##
+##  <#GAPDoc Label="MeetBlist">
+##  <ManSection>
+##  <Func Name="MeetBlist" Arg='blist1, blist2'/>
+##
+##  <Description>
+##  Returns <K>true</K> if there is a position at which both <A>blist1</A>
+##  and <A>blist2</A> contain <K>true</K>, and <K>false</K> otherwise.
+##  It is equivalent to, but faster than
+##  <C>SizeBlist(IntersectionBlist(blist1, blist2)) &lt;&gt; 0</C>.
+##  An error is thrown if the lists do not have the same length.
+##  <Example><![CDATA[
+##  gap> blist1 := [ true, true, true, true ];;
+##  gap> blist2 := [ true, false, true, false ];;
+##  gap> MeetBlist( blist1, blist2 );
+##  true
+##  gap> FlipBlist( blist1 );
+##  gap> MeetBlist( blist1, blist2 );
+##  false
+##  ]]></Example>
+##  </Description>
+##  </ManSection>
+##  <#/GAPDoc>
+##
+DeclareSynonym( "MeetBlist", MEET_BLIST );
+
 #############################################################################
 ##
 #F  FlipBlist( <blist> )
diff --git a/tst/testinstall/kernel/blister.tst b/tst/testinstall/kernel/blister.tst
index 8d9a978cc8..6c3c17d308 100644
--- a/tst/testinstall/kernel/blister.tst
+++ b/tst/testinstall/kernel/blister.tst
@@ -304,17 +304,17 @@ gap> x;
 [ false, false, true, false ]
 
 # FuncMEET_BLIST
-gap> MEET_BLIST(fail, fail);
+gap> MeetBlist(fail, fail);
 Error, MEET_BLIST: <blist1> must be a boolean list (not the value 'fail')
-gap> MEET_BLIST([true,false], fail);
+gap> MeetBlist([true,false], fail);
 Error, MEET_BLIST: <blist2> must be a boolean list (not the value 'fail')
-gap> MEET_BLIST([true,false,true], [true,false]);
+gap> MeetBlist([true,false,true], [true,false]);
 Error, MEET_BLIST: <blist1> must have the same length as <blist2> (lengths are\
  3 and 2)
 gap> x:= [false,true,true,false];;
-gap> MEET_BLIST(x, [true,true,false,false]);
+gap> MeetBlist(x, [true,true,false,false]);
 true
-gap> MEET_BLIST(x, [true,false,false,false]);
+gap> MeetBlist(x, [true,false,false,false]);
 false
 
 # FuncFLIP_BLIST