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Add arithmetic comparison predicates

--- a/builtins.c

+++ b/builtins.c

@@ -46,6 +46,7 @@

 BuiltinProto(builtinsetoutput);

 BuiltinProto(builtinreadterm);

 BuiltinProto(builtinwriteterm);

+BuiltinProto(builtingeq);

 int compareterms(Term *, Term *);

@@ -127,6 +128,8 @@

 		return builtinreadterm;

 	if(Match(L"write_term", 3))

 		return builtinwriteterm;

+	if(Match(L">=", 2))

+		return builtingeq;

 	return nil;

 }

@@ -777,3 +780,32 @@

 	writeterm(stream, options, term);

 	return 1;

 }

+

+int

+builtingeq(Term *goal, Binding **bindings, Module *module)

+{

+	USED(bindings);

+	USED(module);

+	Term *a = goal->children;

+	Term *b = a->next;

+

+	int waserror;

+	Term *aval = aritheval(a, &waserror);

+	if(waserror)

+		Throw(aval);

+	

+	Term *bval = aritheval(b, &waserror);

+	if(waserror)

+		Throw(bval);

+

+	if(aval->tag == IntegerTerm && bval->tag == IntegerTerm)

+		return aval->ival >= bval->ival;

+	else if(aval->tag == FloatTerm && bval->tag == FloatTerm)

+		return aval->dval >= bval->dval;

+	else if(aval->tag == IntegerTerm && bval->tag == FloatTerm)

+		return aval->ival >= bval->dval;

+	else if(aval->tag == FloatTerm && bval->tag == IntegerTerm)

+		return aval->dval >= bval->ival;

+	else

+		return 0;

+}

\ No newline at end of file

--- a/parser.c

+++ b/parser.c

@@ -382,7 +382,7 @@

 	addoperator(700,  Xfx, L"@>=");

 	addoperator(700,  Xfx, L"is");

 	addoperator(700,  Xfx, L"=:=");

-	addoperator(700,  Xfx, L"=\=");

+	addoperator(700,  Xfx, L"=\\=");

 	addoperator(700,  Xfx, L"<");

 	addoperator(700,  Xfx, L"=<");

 	addoperator(700,  Xfx, L">");

--- a/stdlib.pl

+++ b/stdlib.pl

@@ -129,3 +129,24 @@

 write_canonical(S, Term) :-

 	write_term(S, Term, [quoted(true), ignore_ops(true)]).

+% Arithmetic comparisons defined in terms of >=. This is not the most effective way,

+% but it is fine for now.

+

+E1 =:= E2 :-

+	E1 >= E2,

+	E2 >= E1.

+

+E1 =\= E2 :-

+	\+ E1 =:= E2.

+

+E1 < E2 :-

+	E2 >= E1,

+	E1 =\= E2.

+

+E1 =< E2 :-

+	E2 >= E1.

+

+E1 > E2 :-

+	E2 < E1.

+

+