Index: TODO
===================================================================
diff -u -re0419345b49587b5738f87c6d828dfc5ae4b3276 -r3be87f20ac5f89fac33e2db3b95e80c9adfc92d9
--- TODO	(.../TODO)	(revision e0419345b49587b5738f87c6d828dfc5ae4b3276)
+++ TODO	(.../TODO)	(revision 3be87f20ac5f89fac33e2db3b95e80c9adfc92d9)
@@ -4574,25 +4574,24 @@
   instead of 
      o1 info lookup configure syntax
 
-- traits: added ability to trun on verbosity for traits
+- traits: added ability to turn on verbosity for traits
   by using
      nx::configure trait-verbosity on|off
 
 nx.tcl:
 - renamed variable option "-config" to "-configurable"
   to make its intention clearer
 
+- changed multiplicity of mixin, object-mixin, filter, object-filter 
+  from 1..n to 0..n; rationale: when one has a list of eg. mixins,
+  which should be passed, one has to test for the length before
+  passing it, otherwise the empty list would generate an error.
+  Allowing 0..n makes the usage simpler and the program shorter.
 
+
 ========================================================================
 TODO:
 
-- reconsider
-  #? {c1 cget -mixin} ""
-  ? {c1 cget -object-mixin} ""
-
-- reconsider lower multiplicity on 
-  -object-mixin, -mixin...
-
 - handling of "required" in reconfigure (see 
   parameter-object-mixin-dependency in parameters.test)
 - handling of recreate (see regression test for class-level properties)
Index: library/nx/nx.tcl
===================================================================
diff -u -re0419345b49587b5738f87c6d828dfc5ae4b3276 -r3be87f20ac5f89fac33e2db3b95e80c9adfc92d9
--- library/nx/nx.tcl	(.../nx.tcl)	(revision e0419345b49587b5738f87c6d828dfc5ae4b3276)
+++ library/nx/nx.tcl	(.../nx.tcl)	(revision 3be87f20ac5f89fac33e2db3b95e80c9adfc92d9)
@@ -1539,19 +1539,19 @@
   #     filter
 
   ::nx::RelationSlot create ::nx::Object::slot::object-mixin \
-      -multiplicity 1..n \
+      -multiplicity 0..n \
       -methodname "::nx::Object::slot::__object::mixin" \
       -settername "object mixin" -forwardername object-mixin -elementtype mixinreg
   ::nx::RelationSlot create ::nx::Object::slot::object-filter \
       -methodname "::nx::Object::slot::__object::filter" \
-      -multiplicity 1..n \
+      -multiplicity 0..n \
       -settername "object filter" -forwardername object-filter -elementtype filterreg 
   
   ::nx::RelationSlot create ::nx::Class::slot::mixin \
-      -multiplicity 1..n \
+      -multiplicity 0..n \
       -forwardername class-mixin -elementtype mixinreg
   ::nx::RelationSlot create ::nx::Class::slot::filter \
-      -multiplicity 1..n \
+      -multiplicity 0..n \
       -forwardername class-filter -elementtype filterreg
 
   #
Index: tests/info-method.test
===================================================================
diff -u -r625a3e7b5660331938ab739fb28eda3d5540e189 -r3be87f20ac5f89fac33e2db3b95e80c9adfc92d9
--- tests/info-method.test	(.../info-method.test)	(revision 625a3e7b5660331938ab739fb28eda3d5540e189)
+++ tests/info-method.test	(.../info-method.test)	(revision 3be87f20ac5f89fac33e2db3b95e80c9adfc92d9)
@@ -721,7 +721,7 @@
   ? {C info configure syntax} "/::C/ ?-a /value/? ?-b /value/? ?-volatile? ?-noinit? ?-object-mixin /mixinreg .../? ?-class /class/? ?-object-filter /filterreg .../? ?/__initblock/?"
 #  ? {C info configure syntax a} "/::C/ ?-a /value/?"
 
-  ? {C info configure parameters } "-a {-b 1} -volatile:alias,slot=::nx::Object::slot::volatile,slotassign,noarg -noinit:alias,method=::nsf::methods::object::noinit,noarg -object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,1..n -class:class,alias,method=::nsf::methods::object::class -object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,1..n __initblock:cmd,optional,noleadingdash"
+  ? {C info configure parameters } "-a {-b 1} -volatile:alias,slot=::nx::Object::slot::volatile,slotassign,noarg -noinit:alias,method=::nsf::methods::object::noinit,noarg -object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,0..n -class:class,alias,method=::nsf::methods::object::class -object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,0..n __initblock:cmd,optional,noleadingdash"
 
 #  ? {C info parameter list} "-a -b -volatile -noinit -object-mixin -class -object-filter __initblock"
 #  ? {C info parameter names} "a b volatile noinit object-mixin class object-filter __initblock"
Index: tests/info-variable.test
===================================================================
diff -u -r2f6bcca3537584c8ef1f9fc71b230e79d1560504 -r3be87f20ac5f89fac33e2db3b95e80c9adfc92d9
--- tests/info-variable.test	(.../info-variable.test)	(revision 2f6bcca3537584c8ef1f9fc71b230e79d1560504)
+++ tests/info-variable.test	(.../info-variable.test)	(revision 3be87f20ac5f89fac33e2db3b95e80c9adfc92d9)
@@ -35,9 +35,9 @@
 -name
 -volatile:alias,slot=::nx::Object::slot::volatile,slotassign,noarg
 -noinit:alias,method=::nsf::methods::object::noinit,noarg
--object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,1..n
+-object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,0..n
 -class:class,alias,method=::nsf::methods::object::class
--object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,1..n
+-object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,0..n
 __initblock:cmd,optional,noleadingdash"
 
   ? {Person info configure parameters age} "-age:integer"
Index: tests/parameters.test
===================================================================
diff -u -re0419345b49587b5738f87c6d828dfc5ae4b3276 -r3be87f20ac5f89fac33e2db3b95e80c9adfc92d9
--- tests/parameters.test	(.../parameters.test)	(revision e0419345b49587b5738f87c6d828dfc5ae4b3276)
+++ tests/parameters.test	(.../parameters.test)	(revision 3be87f20ac5f89fac33e2db3b95e80c9adfc92d9)
@@ -275,7 +275,7 @@
   C create c1
  
   ? {C eval :__objectparameter} \
-      "{-superclass:class,alias,method=::nsf::methods::class::superclass,1..n ::nx::Object} -mixin:mixinreg,alias,1..n -filter:filterreg,alias,1..n -volatile:alias,slot=::nx::Object::slot::volatile,slotassign,noarg -noinit:alias,method=::nsf::methods::object::noinit,noarg -object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,1..n -class:class,alias,method=::nsf::methods::object::class -object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,1..n __initblock:cmd,optional,noleadingdash"
+      "{-superclass:class,alias,method=::nsf::methods::class::superclass,1..n ::nx::Object} -mixin:mixinreg,alias,0..n -filter:filterreg,alias,0..n -volatile:alias,slot=::nx::Object::slot::volatile,slotassign,noarg -noinit:alias,method=::nsf::methods::object::noinit,noarg -object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,0..n -class:class,alias,method=::nsf::methods::object::class -object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,0..n __initblock:cmd,optional,noleadingdash"
 
   #### TOOD: remove or add
   #? {c1 eval :__objectparameter} \
@@ -307,7 +307,7 @@
       "::D::slot::d ::C::slot::a ::C::slot::b ::C::slot::c"
   
   ? {d1 eval :__objectparameter} \
-      "-d:required -a -b:boolean {-c 1} -volatile:alias,slot=::nx::Object::slot::volatile,slotassign,noarg -noinit:alias,method=::nsf::methods::object::noinit,noarg -object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,1..n -class:class,alias,method=::nsf::methods::object::class -object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,1..n __initblock:cmd,optional,noleadingdash"
+      "-d:required -a -b:boolean {-c 1} -volatile:alias,slot=::nx::Object::slot::volatile,slotassign,noarg -noinit:alias,method=::nsf::methods::object::noinit,noarg -object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,0..n -class:class,alias,method=::nsf::methods::object::class -object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,0..n __initblock:cmd,optional,noleadingdash"
 }
 
 #######################################################
@@ -336,29 +336,29 @@
   D mixin M
 
   ? {d1 eval :__objectparameter} \
-      "-b -m1 -m2 -d:required -a {-c 1} -volatile:alias,slot=::nx::Object::slot::volatile,slotassign,noarg -noinit:alias,method=::nsf::methods::object::noinit,noarg -object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,1..n -class:class,alias,method=::nsf::methods::object::class -object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,1..n __initblock:cmd,optional,noleadingdash" \
+      "-b -m1 -m2 -d:required -a {-c 1} -volatile:alias,slot=::nx::Object::slot::volatile,slotassign,noarg -noinit:alias,method=::nsf::methods::object::noinit,noarg -object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,0..n -class:class,alias,method=::nsf::methods::object::class -object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,0..n __initblock:cmd,optional,noleadingdash" \
     "mixin added"
 
   M mixin M2
 
   ? {d1 eval :__objectparameter} \
-      "-b2 -b -m1 -m2 -d:required -a {-c 1} -volatile:alias,slot=::nx::Object::slot::volatile,slotassign,noarg -noinit:alias,method=::nsf::methods::object::noinit,noarg -object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,1..n -class:class,alias,method=::nsf::methods::object::class -object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,1..n __initblock:cmd,optional,noleadingdash" \
+      "-b2 -b -m1 -m2 -d:required -a {-c 1} -volatile:alias,slot=::nx::Object::slot::volatile,slotassign,noarg -noinit:alias,method=::nsf::methods::object::noinit,noarg -object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,0..n -class:class,alias,method=::nsf::methods::object::class -object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,0..n __initblock:cmd,optional,noleadingdash" \
     "transitive mixin added"
   D mixin ""
   #we should have again the old interface
 
   ? {d1 eval :__objectparameter} \
-      "-d:required -a -b:boolean {-c 1} -volatile:alias,slot=::nx::Object::slot::volatile,slotassign,noarg -noinit:alias,method=::nsf::methods::object::noinit,noarg -object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,1..n -class:class,alias,method=::nsf::methods::object::class -object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,1..n __initblock:cmd,optional,noleadingdash"
+      "-d:required -a -b:boolean {-c 1} -volatile:alias,slot=::nx::Object::slot::volatile,slotassign,noarg -noinit:alias,method=::nsf::methods::object::noinit,noarg -object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,0..n -class:class,alias,method=::nsf::methods::object::class -object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,0..n __initblock:cmd,optional,noleadingdash"
 
   C mixin M
   ? {d1 eval :__objectparameter} \
-      "-b2 -b -m1 -m2 -d:required -a {-c 1} -volatile:alias,slot=::nx::Object::slot::volatile,slotassign,noarg -noinit:alias,method=::nsf::methods::object::noinit,noarg -object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,1..n -class:class,alias,method=::nsf::methods::object::class -object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,1..n __initblock:cmd,optional,noleadingdash" \
+      "-b2 -b -m1 -m2 -d:required -a {-c 1} -volatile:alias,slot=::nx::Object::slot::volatile,slotassign,noarg -noinit:alias,method=::nsf::methods::object::noinit,noarg -object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,0..n -class:class,alias,method=::nsf::methods::object::class -object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,0..n __initblock:cmd,optional,noleadingdash" \
     "mixin added"
   C mixin ""
   #we should have again the old interface
   
   ? {d1 eval :__objectparameter} \
-      "-d:required -a -b:boolean {-c 1} -volatile:alias,slot=::nx::Object::slot::volatile,slotassign,noarg -noinit:alias,method=::nsf::methods::object::noinit,noarg -object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,1..n -class:class,alias,method=::nsf::methods::object::class -object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,1..n __initblock:cmd,optional,noleadingdash" 
+      "-d:required -a -b:boolean {-c 1} -volatile:alias,slot=::nx::Object::slot::volatile,slotassign,noarg -noinit:alias,method=::nsf::methods::object::noinit,noarg -object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,0..n -class:class,alias,method=::nsf::methods::object::class -object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,0..n __initblock:cmd,optional,noleadingdash" 
 }
 
 #######################################################
@@ -1843,13 +1843,13 @@
   nx::Class create M1 {:property b1:required}
   nx::Class create M2 {:property b2:required}
 
-  ? {c1 eval :__objectparameter} "-a1 -volatile:alias,slot=::nx::Object::slot::volatile,slotassign,noarg -noinit:alias,method=::nsf::methods::object::noinit,noarg -object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,1..n -class:class,alias,method=::nsf::methods::object::class -object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,1..n __initblock:cmd,optional,noleadingdash"
+  ? {c1 eval :__objectparameter} "-a1 -volatile:alias,slot=::nx::Object::slot::volatile,slotassign,noarg -noinit:alias,method=::nsf::methods::object::noinit,noarg -object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,0..n -class:class,alias,method=::nsf::methods::object::class -object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,0..n __initblock:cmd,optional,noleadingdash"
   
   c1 object mixin M1
 
   ? {c1 info precedence} "::M1 ::C ::nx::Object"
 
-  ? {c1 eval :__objectparameter} "-b1:required -a1 -volatile:alias,slot=::nx::Object::slot::volatile,slotassign,noarg -noinit:alias,method=::nsf::methods::object::noinit,noarg -object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,1..n -class:class,alias,method=::nsf::methods::object::class -object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,1..n __initblock:cmd,optional,noleadingdash"
+  ? {c1 eval :__objectparameter} "-b1:required -a1 -volatile:alias,slot=::nx::Object::slot::volatile,slotassign,noarg -noinit:alias,method=::nsf::methods::object::noinit,noarg -object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,0..n -class:class,alias,method=::nsf::methods::object::class -object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,0..n __initblock:cmd,optional,noleadingdash"
 
   #
   # Invalidate the object parameter and expect that the per-class
@@ -1952,7 +1952,7 @@
       "::C::slot::a1 ::nx::Object::slot::volatile ::nx::Object::slot::__initblock ::nx::Object::slot::noinit ::nx::Object::slot::object-mixin ::nx::Object::slot::class ::nx::Object::slot::object-filter"
 
   ? {c1 eval :__objectparameter} \
-      "-a2 -b1:required -a1 -volatile:alias,slot=::nx::Object::slot::volatile,slotassign,noarg -noinit:alias,method=::nsf::methods::object::noinit,noarg -object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,1..n -class:class,alias,method=::nsf::methods::object::class -object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,1..n __initblock:cmd,optional,noleadingdash"
+      "-a2 -b1:required -a1 -volatile:alias,slot=::nx::Object::slot::volatile,slotassign,noarg -noinit:alias,method=::nsf::methods::object::noinit,noarg -object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,0..n -class:class,alias,method=::nsf::methods::object::class -object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,0..n __initblock:cmd,optional,noleadingdash"
 
   #
   # invalidate object parameter and expect that the per-class mixin
@@ -1968,7 +1968,7 @@
       "::C::slot::a1 ::nx::Object::slot::volatile ::nx::Object::slot::__initblock ::nx::Object::slot::noinit ::nx::Object::slot::object-mixin ::nx::Object::slot::class ::nx::Object::slot::object-filter"
 
 
-  ? {c1 eval :__objectparameter} "-a2 -b1:required -a1 -volatile:alias,slot=::nx::Object::slot::volatile,slotassign,noarg -noinit:alias,method=::nsf::methods::object::noinit,noarg -object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,1..n -class:class,alias,method=::nsf::methods::object::class -object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,1..n __initblock:cmd,optional,noleadingdash"
+  ? {c1 eval :__objectparameter} "-a2 -b1:required -a1 -volatile:alias,slot=::nx::Object::slot::volatile,slotassign,noarg -noinit:alias,method=::nsf::methods::object::noinit,noarg -object-mixin:mixinreg,alias,method=::nx::Object::slot::__object::mixin,0..n -class:class,alias,method=::nsf::methods::object::class -object-filter:filterreg,alias,method=::nx::Object::slot::__object::filter,0..n __initblock:cmd,optional,noleadingdash"
 
   # should not require b1
   ? {C create c2} ::c2