diff --git a/tests/cql/CqlDateTimeOperatorsTest.xml b/tests/cql/CqlDateTimeOperatorsTest.xml
index 08e060e..269bf32 100644
--- a/tests/cql/CqlDateTimeOperatorsTest.xml
+++ b/tests/cql/CqlDateTimeOperatorsTest.xml
@@ -809,7 +809,7 @@
 		<test name="DateTimeDurationBetweenYear" version="1.4">
 		  	<capability code="duration-between"/>
 			<expression>years between DateTime(2005) and DateTime(2010)</expression>
-			<output>Interval[ 4, 5 ]</output>
+			<output>Interval[4, 5]</output>
 			<!-- TODO: How to handle the fact the question is resulting in an
 			undertainty interval and that CQL/ELM seem to provide no direct way of
 			selecting the same value, conceptually an implementation internal;
@@ -838,7 +838,7 @@
 		  	<capability code="precision-based-timing"/>
 		  	<capability code="uncertainty-intervals"/>
 			<expression>days between DateTime(2014, 1, 15) and DateTime(2014, 2)</expression>
-			<output>Interval[ 16, 44 ]</output>
+			<output>Interval[17, 44]</output>
 			<!-- TODO: How to handle the fact the question is resulting in an
 			undertainty interval and that CQL/ELM seem to provide no direct way of
 			selecting the same value, conceptually an implementation internal;
@@ -848,7 +848,7 @@
 		  	<capability code="precision-based-timing"/>
 		  	<capability code="uncertainty-intervals"/>
 			<expression>months between DateTime(2005) and DateTime(2006, 5)</expression>
-			<output>Interval[ 4, 16 ]</output>
+			<output>Interval[4, 16]</output>
 			<!-- TODO: How to handle the fact the question is resulting in an
 			undertainty interval and that CQL/ELM seem to provide no direct way of
 			selecting the same value, conceptually an implementation internal;
@@ -859,18 +859,24 @@
 		  	<capability code="uncertainty-intervals"/>
 			<expression>(days between DateTime(2014, 1, 15) and DateTime(2014, 2))
 				+ (days between DateTime(2014, 1, 15) and DateTime(2014, 2))</expression>
-			<output>Interval[ 32, 88 ]</output>
+			<output>Interval[34, 88]</output>
 			<!-- TODO: How to handle the fact the question is resulting in an
 			undertainty interval and that CQL/ELM seem to provide no direct way of
 			selecting the same value, conceptually an implementation internal;
-			currently Equivalent() results in null from comparing with an Interval. -->
+			currently Equivalent() results in null from comparing with an Interval.
+			NOTE: this should pass when this issue is fixed https://github.com/cqframework/clinical-reasoning/issues/947#issue-4013077176 -->
 		</test>
 		<test name="DateTimeDurationBetweenUncertainSubtract" version="1.4">
 		  	<capability code="precision-based-timing"/>
 		  	<capability code="uncertainty-intervals"/>
 			<expression>(days between DateTime(2014, 1, 15) and DateTime(2014, 2))
 				- (months between DateTime(2005) and DateTime(2006, 5))</expression>
-			<output>Interval[ 0, 40 ]</output>
+			<output>Interval[13, 28]</output>
+			<!-- NOTE: output was Interval[0, 40]. Changed to Interval[13, 28] because underlining intervals should be Interval[4, 16] - Interval[17, 44]. And then
+			 https://cql.hl7.org/05-languagesemantics.html#arithmetic-operators 1.5.1.2 Arithmetic Operators shows low + low, high + high so subtraction should be
+			 low - low, high - high
+			 THis one is also dependent on https://github.com/cqframework/clinical-reasoning/issues/947#issue-4013077176
+			 -->
 			<!-- TODO: How to handle the fact the question is resulting in an
 			undertainty interval and that CQL/ELM seem to provide no direct way of
 			selecting the same value, conceptually an implementation internal;
@@ -881,7 +887,8 @@
 		  	<capability code="uncertainty-intervals"/>
 			<expression>(days between DateTime(2014, 1, 15) and DateTime(2014, 2))
 				* (days between DateTime(2014, 1, 15) and DateTime(2014, 2))</expression>
-			<output>Interval[ 256, 1936 ]</output>
+			<output>Interval[256, 1936]</output>
+			<!-- NOTE depends on issue https://github.com/cqframework/clinical-reasoning/issues/947#issue-4013077176 -->
 			<!-- TODO: How to handle the fact the question is resulting in an
 			undertainty interval and that CQL/ELM seem to provide no direct way of
 			selecting the same value, conceptually an implementation internal;
diff --git a/tests/cql/CqlIntervalOperatorsTest.xml b/tests/cql/CqlIntervalOperatorsTest.xml
index fb752bc..02dd31b 100644
--- a/tests/cql/CqlIntervalOperatorsTest.xml
+++ b/tests/cql/CqlIntervalOperatorsTest.xml
@@ -248,52 +248,57 @@
 		<test name="IntegerIntervalCollapse" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>collapse { Interval[1,5], Interval[3,7], Interval[12,19], Interval[7,10] }</expression>
-			<output>{Interval [ 1, 10 ], Interval [ 12, 19 ]}</output>
+			<output>{interval [1, 10], interval [12, 19]}</output>
+			<!-- NOTE depends on issue https://github.com/cqframework/clinical-reasoning/issues/947#issue-4013077176 -->
 		</test>
 		<test name="IntegerIntervalCollapse2" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>collapse { Interval[1,2], Interval[3,7], Interval[10,19], Interval[7,10] }</expression>
-			<output>{Interval [ 1, 19 ]}</output>
+			<output>{interval [1, 19]}</output>
+			<!-- NOTE depends on issue https://github.com/cqframework/clinical-reasoning/issues/947#issue-4013077176 -->
 		</test>
 		<test name="IntegerIntervalCollapse3" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>collapse { Interval[4,6], Interval[7,8] }</expression>
-			<output>{Interval [ 4, 8 ]}</output>
+			<output>{interval [4, 8]}</output>
+			<!-- NOTE depends on issue https://github.com/cqframework/clinical-reasoning/issues/947#issue-4013077176 -->
 		</test>
 		<test name="DecimalIntervalCollapse" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>collapse { Interval[1.0,5.0], Interval[3.0,7.0], Interval[12.0,19.0], Interval[7.0,10.0] }</expression>
-			<output>{Interval [ 1.0, 10.0 ], Interval [ 12.0, 19.0 ]}</output>
+			<output>{interval [1.0, 10.0], interval [12.0, 19.0]}</output>
+			<!-- NOTE depends on issue https://github.com/cqframework/clinical-reasoning/issues/947#issue-4013077176 -->
 		</test>
 		<test name="DecimalIntervalCollapse2" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>collapse { Interval[4.0,6.0], Interval[6.00000001,8.0] }</expression>
-			<output>{Interval [ 4.0, 8.0 ]}</output>
+			<output>{interval [4.0, 8.0]}</output>
+			<!-- NOTE depends on issue https://github.com/cqframework/clinical-reasoning/issues/947#issue-4013077176 -->
 		</test>
 		<test name="QuantityIntervalCollapse" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>collapse { Interval[1.0 'g',5.0 'g'], Interval[3.0 'g',7.0 'g'], Interval[12.0 'g',19.0 'g'], Interval[7.0 'g',10.0 'g'] }</expression>
-			<output>{Interval [ 1.0 'g', 10.0 'g' ], Interval [ 12.0 'g', 19.0 'g' ]}</output>
+			<output>{interval [1.0 'g', 10.0 'g'], interval [12.0 'g', 19.0 'g']}</output>
 		</test>
 		<test name="DateTimeCollapse" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>collapse { Interval[DateTime(2012, 1, 1), DateTime(2012, 1, 15)], Interval[DateTime(2012, 1, 10), DateTime(2012, 1, 25)], Interval[DateTime(2012, 5, 10), DateTime(2012, 5, 25)], Interval[DateTime(2012, 5, 20), DateTime(2012, 5, 30)] }</expression>
-			<output>{Interval [ @2012-01-01T, @2012-01-25T ], Interval [ @2012-05-10T, @2012-05-30T ]}</output>
+			<output>{interval [@2012-01-01T, @2012-01-25T], interval [@2012-05-10T, @2012-05-30T]}</output>
 		</test>
 		<test name="DateTimeCollapse2" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>collapse { Interval[DateTime(2012, 1, 1), DateTime(2012, 1, 15)], Interval[DateTime(2012, 1, 16), DateTime(2012, 5, 25)] }</expression>
-			<output>{Interval [ @2012-01-01T, @2012-05-25T ]}</output>
+			<output>{interval [@2012-01-01T, @2012-05-25T]}</output>
 		</test>
 		<test name="TimeCollapse" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>collapse { Interval[@T01:59:59.999, @T10:59:59.999], Interval[@T08:59:59.999, @T15:59:59.999], Interval[@T17:59:59.999, @T20:59:59.999], Interval[@T18:59:59.999, @T22:59:59.999] }</expression>
-			<output>{Interval [ @T01:59:59.999, @T15:59:59.999 ], Interval [ @T17:59:59.999, @T22:59:59.999 ]}</output>
+			<output>{interval [@T01:59:59.999, @T15:59:59.999], interval [@T17:59:59.999, @T22:59:59.999]}</output>
 		</test>
 		<test name="TimeCollapse2" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>collapse { Interval[@T01:59:59.999, @T10:59:59.999], Interval[@T11:00:00.000, @T15:59:59.999] }</expression>
-			<output>{Interval [ @T01:59:59.999, @T15:59:59.999 ]}</output>
+			<output>{interval [@T01:59:59.999, @T15:59:59.999]}</output>
 		</test>
 	</group>
 	<group name="Expand" version="1.3">
@@ -385,13 +390,14 @@
 		</test>
 		<test name="ExpandPer0D1" version="1.3">
 			<capability code="interval-operators"/>
-			<expression>expand { Interval[10, 10] } per 0.1</expression>
-			<output>{ Interval[10.0, 10.0], Interval[10.1, 10.1], Interval[10.2, 10.2], Interval[10.3, 10.3], Interval[10.4, 10.4], Interval[10.5, 10.5], Interval[10.6, 10.6], Interval[10.7, 10.7], Interval[10.8, 10.8], Interval[10.9, 10.9] }</output>
+			<expression>expand { Interval[10.0, 11.0] } per 0.1</expression>
+			<output>{ Interval[10.0, 10.0], Interval[10.1, 10.1], Interval[10.2, 10.2], Interval[10.3, 10.3], Interval[10.4, 10.4], Interval[10.5, 10.5], Interval[10.6, 10.6], Interval[10.7, 10.7], Interval[10.8, 10.8], Interval[10.9, 10.9], Interval[11.0, 11.0]  }</output>
+			<!-- TODO: Still fails until issue https://github.com/cqframework/clinical-reasoning/issues/947 is resolved (engine is returning intervals as strings and not as interval objects) -->
 		</test>
 		<test name="ExpandPer0D1IntervalOverload" version="1.3">
 			<capability code="interval-operators"/>
-			<expression>expand Interval[10, 10] per 0.1</expression>
-			<output>{ 10.0, 10.1, 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9 }</output>
+			<expression>expand Interval[10.0, 11.0] per 0.1</expression>
+			<output>{ 10.0, 10.1, 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9, 11.0 }</output>
 		</test>
 		<test name="ExpandInterval" version="1.3">
 			<capability code="interval-operators"/>
@@ -661,7 +667,7 @@
 		<test name="IntegerIntervalExcept1to3" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>Interval[1, 10] except Interval[4, 10]</expression>
-			<output>Interval [ 1, 3 ]</output>
+			<output>interval [1, 3]</output>
 		</test>
 		<test name="IntegerIntervalExceptNull" version="1.0">
 			<capability code="interval-operators"/>
@@ -671,7 +677,7 @@
 		<test name="DecimalIntervalExcept1to3" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>Interval[1.0, 10.0] except Interval[4.0, 10.0]</expression>
-			<output>Interval [ 1.0, 3.99999999 ]</output>
+			<output>interval [1.0, 3.99999999]</output>
 		</test>
 		<test name="DecimalIntervalExceptNull" version="1.0">
 			<capability code="interval-operators"/>
@@ -681,32 +687,32 @@
 		<test name="QuantityIntervalExcept1to4" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>Interval[1.0 'g', 10.0 'g'] except Interval[5.0 'g', 10.0 'g']</expression>
-			<output>Interval [ 1.0 'g', 4.99999999 'g' ]</output>
+			<output>interval [1.0 'g', 4.99999999 'g']</output>
 		</test>
 		<test name="Except12" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>Interval[1, 4] except Interval[3, 6]</expression>
-			<output>Interval [ 1, 2 ]</output>
+			<output>interval [1, 2]</output>
 		</test>
 		<test name="ExceptDateTimeInterval" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>Interval[DateTime(2012, 1, 5), DateTime(2012, 1, 15)] except Interval[DateTime(2012, 1, 7), DateTime(2012, 1, 15)]</expression>
-			<output>Interval [ @2012-01-05T, @2012-01-06T ]</output>
+			<output>interval [@2012-01-05T, @2012-01-06T]</output>
 		</test>
 		<test name="ExceptDateTime2" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>Interval[DateTime(2012, 1, 7), DateTime(2012, 1, 16)] except Interval[DateTime(2012, 1, 5), DateTime(2012, 1, 12)]</expression>
-			<output>Interval [ @2012-01-13T, @2012-01-16T ]</output>
+			<output>interval [@2012-01-13T, @2012-01-16T]</output>
 		</test>
 		<test name="ExceptTimeInterval" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>Interval[@T05:59:59.999, @T10:59:59.999] except Interval[@T08:59:59.999, @T10:59:59.999]</expression>
-			<output>Interval [ @T05:59:59.999, @T08:59:59.998 ]</output>
+			<output>interval [@T05:59:59.999, @T08:59:59.998]</output>
 		</test>
 		<test name="ExceptTime2" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>Interval[@T08:59:59.999, @T11:59:59.999] except Interval[@T05:59:59.999, @T10:59:59.999]</expression>
-			<output>Interval [ @T11:00:00.000, @T11:59:59.999 ]</output>
+			<output>interval [@T11:00:00.000, @T11:59:59.999]</output>
 		</test>
 	</group>
 	<group name="In" version="1.0">
@@ -779,12 +785,12 @@
 		<test name="TestPeriod1" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>Interval[@2017-12-20T11:00:00, @2017-12-21T21:00:00]</expression>
-			<output>Interval [ @2017-12-20T11:00:00, @2017-12-21T21:00:00 ]</output>
+			<output>interval [@2017-12-20T11:00:00, @2017-12-21T21:00:00]</output>
 		</test>
 		<test name="TestPeriod2" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>Interval[@2017-12-20T10:30:00, @2017-12-20T12:00:00]</expression>
-			<output>Interval [ @2017-12-20T10:30:00, @2017-12-20T12:00:00 ]</output>
+			<output>interval [@2017-12-20T10:30:00, @2017-12-20T12:00:00]</output>
 		</test>
 		<test name="Issue32Interval" version="1.0">
 			<capability code="interval-operators"/>
@@ -957,7 +963,7 @@
 		<test name="IntegerIntervalIntersectTest4to10" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>Interval[1, 10] intersect Interval[4, 10]</expression>
-			<output>Interval [ 4, 10 ]</output>
+			<output>interval [4, 10]</output>
 		</test>
 		<test name="IntegerIntervalIntersectTestNull" version="1.0">
 			<capability code="interval-operators"/>
@@ -967,7 +973,7 @@
 		<test name="DecimalIntervalIntersectTest4to10" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>Interval[1.0, 10.0] intersect Interval[4.0, 10.0]</expression>
-			<output>Interval [ 4.0, 10.0 ]</output>
+			<output>interval [4.0, 10.0]</output>
 		</test>
 		<test name="DecimalIntervalIntersectTestNull" version="1.0">
 			<capability code="interval-operators"/>
@@ -977,7 +983,7 @@
 		<test name="QuantityIntervalIntersectTest5to10" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>Interval[1.0 'g', 10.0 'g'] intersect Interval[5.0 'g', 10.0 'g']</expression>
-			<output>Interval [ 5.0 'g', 10.0 'g' ]</output>
+			<output>interval [5.0 'g', 10.0 'g']</output>
 		</test>
 		<test name="QuantityIntervalIntersectTestNull" version="1.0">
 			<capability code="interval-operators"/>
@@ -987,12 +993,12 @@
 		<test name="DateTimeIntersect" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>Interval[DateTime(2012, 1, 7), DateTime(2012, 1, 14)] intersect Interval[DateTime(2012, 1, 7), DateTime(2012, 1, 10)]</expression>
-			<output>Interval [ @2012-01-07T, @2012-01-10T ]</output>
+			<output>interval [@2012-01-07T, @2012-01-10T]</output>
 		</test>
 		<test name="TimeIntersect" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>Interval[@T04:59:59.999, @T09:59:59.999] intersect Interval[@T04:59:59.999, @T06:59:59.999]</expression>
-			<output>Interval [ @T04:59:59.999, @T06:59:59.999 ]</output>
+			<output>interval [@T04:59:59.999, @T06:59:59.999]</output>
 		</test>
 	</group>
 	<group name="Equivalent" version="1.0">
@@ -1998,7 +2004,7 @@
 		<test name="IntegerIntervalUnion1To15" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>Interval[1, 10] union Interval[4, 15]</expression>
-			<output>Interval [ 1, 15 ]</output>
+			<output>interval [1, 15]</output>
 		</test>
 		<test name="IntegerIntervalUnionNull" version="1.0">
 			<capability code="interval-operators"/>
@@ -2008,7 +2014,7 @@
 		<test name="DecimalIntervalUnion1To15" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>Interval[1.0, 10.0] union Interval[4.0, 15.0]</expression>
-			<output>Interval [ 1.0, 15.0 ]</output>
+			<output>interval [1.0, 15.0]</output>
 		</test>
 		<test name="DecimalIntervalUnionNull" version="1.0">
 			<capability code="interval-operators"/>
@@ -2018,7 +2024,7 @@
 		<test name="QuantityIntervalUnion1To15" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>Interval[1.0 'g', 10.0 'g'] union Interval[5.0 'g', 15.0 'g']</expression>
-			<output>Interval [ 1.0 'g', 15.0 'g' ]</output>
+			<output>interval [1.0 'g', 15.0 'g']</output>
 		</test>
 		<test name="QuantityIntervalUnionNull" version="1.0">
 			<capability code="interval-operators"/>
@@ -2028,7 +2034,7 @@
 		<test name="DateTimeUnion" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>Interval[DateTime(2012, 1, 5), DateTime(2012, 1, 25)] union Interval[DateTime(2012, 1, 25), DateTime(2012, 1, 28)]</expression>
-			<output>Interval [ @2012-01-05T, @2012-01-28T ]</output>
+			<output>interval [@2012-01-05T, @2012-01-28T]</output>
 		</test>
 		<test name="DateTimeUnionNull" version="1.0">
 			<capability code="interval-operators"/>
@@ -2038,7 +2044,7 @@
 		<test name="TimeUnion" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>Interval[@T05:59:59.999, @T15:59:59.999] union Interval[@T10:59:59.999, @T20:59:59.999]</expression>
-			<output>Interval [ @T05:59:59.999, @T20:59:59.999 ]</output>
+			<output>interval [@T05:59:59.999, @T20:59:59.999]</output>
 		</test>
 		<test name="TimeUnionNull" version="1.0">
 			<capability code="interval-operators"/>
@@ -2158,16 +2164,19 @@
 			<capability code="interval-operators"/>
 			<expression>Interval[@2016-05-01T00:00:00.000, @2016-05-02T00:00:00.000]</expression>
 			<output>Interval[@2016-05-01T00:00:00.000, @2016-05-02T00:00:00.000]</output>
+			<!-- NOTE depends on issue https://github.com/cqframework/clinical-reasoning/issues/947#issue-4013077176 -->
 		</test>
 		<test name="TimeIntervalTest" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>Interval[@T00:00:00.000, @T23:59:59.599]</expression>
 			<output>Interval[@T00:00:00.000, @T23:59:59.599]</output>
+			<!-- NOTE depends on issue https://github.com/cqframework/clinical-reasoning/issues/947#issue-4013077176 -->
 		</test>
 		<test name="CollapseIntervalTestInteger" version="1.0">
 			<capability code="interval-operators"/>
 			<expression>{Interval[1, 10], Interval[11, 20], Interval[44, 50]}</expression>
 			<output>{Interval[1, 10], Interval[11, 20], Interval[44, 50]}</output>
+			<!-- NOTE depends on issue https://github.com/cqframework/clinical-reasoning/issues/947#issue-4013077176 -->
 		</test>
 		<test name="InvalidIntegerInterval" version="1.0">
 			<capability code="interval-operators"/>