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In Issue #347 it is shown that set equality fails after applying a map to a set:

fricas
A:Set Integer := set [-2,-1,0] (1)
Type: Set(Integer)
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B:Set Integer := set [0,1,4] (2)
Type: Set(Integer)
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C:=map(x +-> x^2,A) (3)
Type: Set(Integer)
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test(C=B) (4)
Type: Boolean

A possible fix is given in #347 for Sets whose members have OrderedSet.

## A More Ambitious Fix

As suggested by the documentation in the code for Set domain, sets must be sorted based some ordering applicable to all Axiom object. One such order can be defined by the SXHASH value (ref). For example:

   order(x:S,y:S):Boolean == integer(SXHASH(x)$Lisp)$SExpression<integer(SXHASH(y)$Lisp)$SExpression

map_!(f,s) ==
map_!(f,s)$Rep sort_!(order,s)$Rep
removeDuplicates_! s

construct l ==
zero?(n := #l) => empty()
a := new(n, first l)
for i in minIndex(a).. for x in l repeat a.i := x
removeDuplicates_! sort_!(order,a)


although the ordering may fail to be total because of collisions.

A better ordering is given by the lexical ordering function LEXGREATERP defined in the Axiom interpreter code ggreater.lisp :

   order(x:S,y:S):Boolean == null? LEXGREATERP(a,b)$Lisp  This ordering is compatible with the "natural" ordering in each domain if the domain has OrderedSet Modified Domain Set spad )abbrev domain SET Set ++ Author: Michael Monagan; revised by Richard Jenks ++ Date Created: August 87 through August 88 ++ Date Previously Updated: May 1991 ++ Basic Operations: ++ Related Constructors: ++ Also See: ++ AMS Classifications: ++ Keywords: ++ References: ++ Description: ++ A set over a domain D models the usual mathematical notion of a finite set ++ of elements from D. ++ Sets are unordered collections of distinct elements ++ (that is, order and duplication does not matter). ++ The notation \spad{set [a,b,c]} can be used to create ++ a set and the usual operations such as union and intersection are available ++ to form new sets. ++ In our implementation, \Language{} maintains the entries in ++ sorted order. Specifically, the parts function returns the entries ++ as a list in ascending order and ++ the extract operation returns the maximum entry. ++ Given two sets s and t where \spad{#s = m} and \spad{#t = n}, ++ the complexity of ++ \spad{s = t} is \spad{O(min(n,m))} ++ \spad{s < t} is \spad{O(max(n,m))} ++ \spad{union(s,t)}, \spad{intersect(s,t)}, \spad{minus(s,t)}, \spad{symmetricDifference(s,t)} is \spad{O(max(n,m))} ++ \spad{member(x,t)} is \spad{O(n log n)} ++ \spad{insert(x,t)} and \spad{remove(x,t)} is \spad{O(n)} Set(S:SetCategory): FiniteSetAggregate S == add Rep := FlexibleArray(S) # s == _#$Rep s
brace()   == empty()
set()     == empty()
empty()   == empty()$Rep copy s == copy(s)$Rep
parts s   == parts(s)$Rep inspect s == (empty? s => error "Empty set"; s(maxIndex s)) extract! s == x := inspect s delete!(s, maxIndex s) x find(f, s) == find(f, s)$Rep
map(f, s) == map!(f,copy s)
reduce(f, s) == reduce(f, s)$Rep reduce(f, s, x) == reduce(f, s, x)$Rep
reduce(f, s, x, y) == reduce(f, s, x, y)$Rep if S has ConvertibleTo InputForm then convert(x:%):InputForm == convert [convert("set"::Symbol)@InputForm, convert(parts x)@InputForm] order(x:S,y:S):Boolean == null?(LEXGREATERP(x,y)$Lisp)$SExpression -- Not as good? -- integer(SXHASH(x)$Lisp)$SExpression<integer(SXHASH(y)$Lisp)$SExpression map!(f, s) == map!(f, s)$Rep
sort!(order, s)$Rep removeDuplicates! s construct l == zero?(n := #l) => empty() a := new(n, first l) for i in minIndex(a).. for x in l repeat a.i := x removeDuplicates! sort!(order, a) if S has OrderedSet then s = t == s =$Rep t
max s == inspect s
min s == (empty? s => error "Empty set"; s(minIndex s))
insert!(x, s) ==
n := inc maxIndex s
k := minIndex s
while k < n and x > s.k repeat k := inc k
k < n and s.k = x => s
insert!(x, s, k)
member?(x, s) == -- binary search
empty? s => false
t := maxIndex s
b := minIndex s
while b < t repeat
m := (b+t) quo 2
if x > s.m then b := m+1 else t := m
x = s.t
remove!(x:S, s:%) ==
n := inc maxIndex s
k := minIndex s
while k < n and x > s.k repeat k := inc k
k < n and x = s.k => delete!(s, k)
s
-- the set operations are implemented as variations of merging
intersect(s, t) ==
m := maxIndex s
n := maxIndex t
i := minIndex s
j := minIndex t
r := empty()
while i <= m and j <= n repeat
s.i = t.j => (concat!(r, s.i); i := i+1; j := j+1)
if s.i < t.j then i := i+1 else j := j+1
r
difference(s:%, t:%) ==
m := maxIndex s
n := maxIndex t
i := minIndex s
j := minIndex t
r := empty()
while i <= m and j <= n repeat
s.i = t.j => (i := i+1; j := j+1)
s.i < t.j => (concat!(r, s.i); i := i+1)
j := j+1
while i <= m repeat (concat!(r, s.i); i := i+1)
r
symmetricDifference(s, t) ==
m := maxIndex s
n := maxIndex t
i := minIndex s
j := minIndex t
r := empty()
while i <= m and j <= n repeat
s.i < t.j => (concat!(r, s.i); i := i+1)
s.i > t.j => (concat!(r, t.j); j := j+1)
i := i+1; j := j+1
while i <= m repeat (concat!(r, s.i); i := i+1)
while j <= n repeat (concat!(r, t.j); j := j+1)
r
subset?(s, t) ==
m := maxIndex s
n := maxIndex t
m > n => false
i := minIndex s
j := minIndex t
while i <= m and j <= n repeat
s.i = t.j => (i := i+1; j := j+1)
s.i > t.j => j := j+1
return false
i > m
union(s:%, t:%) ==
m := maxIndex s
n := maxIndex t
i := minIndex s
j := minIndex t
r := empty()
while i <= m and j <= n repeat
s.i = t.j => (concat!(r, s.i); i := i+1; j := j+1)
s.i < t.j => (concat!(r, s.i); i := i+1)
(concat!(r, t.j); j := j+1)
while i <= m repeat (concat!(r, s.i); i := i+1)
while j <= n repeat (concat!(r, t.j); j := j+1)
r
else
insert!(x, s) ==
for k in minIndex s .. maxIndex s repeat
s.k = x => return s
insert!(x, s, inc maxIndex s)
remove!(x:S, s:%) ==
n := inc maxIndex s
k := minIndex s
while k < n repeat
x = s.k => return delete!(s, k)
k := inc k
s
   Compiling FriCAS source code from file
using old system compiler.
SET abbreviates domain Set
------------------------------------------------------------------------
initializing NRLIB SET for Set
compiling into NRLIB SET
compiling exported # : $-> NonNegativeInteger ;;; *** |SET;#;$Nni;1| REDEFINED
Time: 0.02 SEC.
************* USER ERROR **********
available signatures for brace:
NONE
NEED brace: () -> ?
****** comp fails at level 1 with expression: ******
((DEF (|brace|) (NIL) (NIL) (|empty|)))
****** level 1  ******
$x:= (DEF (brace) (NIL) (NIL) (empty))$m:= $EmptyMode$f:=
((((|#| #) (< #) (<= #) (= #) ...)))
>> Apparent user error:
unspecified error

Retest

fricas
A2:Set Integer := set [-2,-1,0] (5)
Type: Set(Integer)
fricas
B2:Set Integer := set [0,1,4] (6)
Type: Set(Integer)
fricas
C2:=map(x +-> x^2,A) (7)
Type: Set(Integer)
fricas
test(B2=C2) (8)
Type: Boolean

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)set message any off
showTypeInOutput true;
Type: String

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Set Any has OrderedSet (9)
Type: Boolean
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B5:Set Any:=B (10)
Type: Set(Any)
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C5:Set Any:=C (11)
Type: Set(Any)
fricas
test(B5=C5) (12)
Type: Boolean

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