rule R1
{
  from
    e: IN!Element
    (e.name='root')
  to
    r: OUT!Root
    ....
}

rule R2
{
  from
    e: IN!Element
    (e.name='operation')
  to
    op: OUT!Operation
    ....
}

rule R
{
  from
    d_in: In!Diagram
  to
    d_out: OUT!Diagram
    (
      elements <- d_in.elements->select(e|e.name='root')
			       ->collect(e|thisModule.resolveTemp(e, 'r'))
	          ->union(d_in.elements->select(e|e.name='operation')
				       ->collect(e|thisModule.resolveTemp(e, 'op'))
}

rule R
{
  from
    d_in: In!Diagram
  to
    d_out: OUT!Diagram
    (
      elements <- d_in.elements->collect(e|thisModule.resolveTemp(e, 'r'))
		  ->union(d_in.elements->collect(e|thisModule.resolveTemp(e, 'op'))
		  ->excluding(OclUndefined)
    )
}

--- Returns the same as thisModule.resolveTemp(var : OclAny, rule_name : String, target_pattern_name : String),
--- except that it returns OclUndefined if no trace exists instead of throwing an error.
helper def : resolveIfExists(var : Sequence(OclAny), rule_name : String, target_pattern_name : String) : OclAny =
    let tr : OclAny = thisModule.traces.getLinksByRule(rule_name, false) in
    if tr.oclIsUndefined() then
    	OclUndefined
    else
    	let sel : OclAny = tr.getUniqueSourceElements(var) in
        if sel.oclIsUndefined() then
        	OclUndefined
        else
        	let te : OclAny = sel.getSourceElements().get(0).getSourceOf().getTargetElement(target_pattern_name) in
            if te.oclIsUndefined() then
            	OclUndefined
            else
            	te.getObject()
            endif
        endif
       endif;