diff --git a/convex-core/src/main/java/convex/core/data/ACollection.java b/convex-core/src/main/java/convex/core/data/ACollection.java
index a076c3f8f..f078f1ed4 100644
--- a/convex-core/src/main/java/convex/core/data/ACollection.java
+++ b/convex-core/src/main/java/convex/core/data/ACollection.java
@@ -206,7 +206,7 @@ public Object[] toArray() {
 	 * @return The updated collection
 	 */
 	@Override
-	public abstract <R extends ACell> ACollection<R> conj(R x);
+	public abstract ACollection<T> conj(ACell x);
 	
 	/**
 	 * Maps a function over a collection, applying it to each element in turn.
diff --git a/convex-core/src/main/java/convex/core/data/ADataStructure.java b/convex-core/src/main/java/convex/core/data/ADataStructure.java
index 629d3baa4..7d34ff07b 100644
--- a/convex-core/src/main/java/convex/core/data/ADataStructure.java
+++ b/convex-core/src/main/java/convex/core/data/ADataStructure.java
@@ -56,7 +56,6 @@ public final boolean isEmpty() {
 		return isCVMValue();
 	}
 
-
 	/**
 	 * Adds an element to this data structure, in the natural manner defined by the
 	 * general data structure type. e.g. append at the end of a vector.
@@ -65,7 +64,7 @@ public final boolean isEmpty() {
 	 * @param x New element to add
 	 * @return The updated data structure, or null if a failure occurred due to invalid element type
 	 */
-	public abstract <R extends ACell> ADataStructure<R> conj(R x);
+	public abstract ADataStructure<E> conj(ACell x);
 	
 	/**
 	 * Adds multiple elements to this data structure, in the natural manner defined by the
@@ -77,10 +76,9 @@ public final boolean isEmpty() {
 	 * @param xs New elements to add
 	 * @return The updated data structure, or null if a failure occurred due to invalid element types
 	 */
-	@SuppressWarnings("unchecked")
-	public <R extends ACell> ADataStructure<R> conjAll(ACollection<R> xs) {
-		ADataStructure<R> result=(ADataStructure<R>) this;
-		for (R x: xs) {
+	public ADataStructure<E> conjAll(ACollection<? extends E> xs) {
+		ADataStructure<E> result=this;
+		for (E x: xs) {
 			result=result.conj(x);
 			if (result==null) return null;
 		}
diff --git a/convex-core/src/main/java/convex/core/data/AHashSet.java b/convex-core/src/main/java/convex/core/data/AHashSet.java
index 1c2e508a0..e6cf94493 100644
--- a/convex-core/src/main/java/convex/core/data/AHashSet.java
+++ b/convex-core/src/main/java/convex/core/data/AHashSet.java
@@ -21,8 +21,8 @@ protected AHashSet(long count) {
 	protected abstract AHashSet<T> mergeWith(AHashSet<T> b, int setOp, int shift);
 
 	@SuppressWarnings("unchecked")
-	public <R extends ACell> ASet<R> includeAll(ASet<R> elements) {
-		return (ASet<R>) mergeWith((AHashSet<T>) elements,OP_UNION);
+	public AHashSet<T> includeAll(ASet<? extends T> elements) {
+		return mergeWith((AHashSet<T>) elements,OP_UNION);
 	};
 	
 	protected final int reverseOp(int setOp) {
@@ -62,10 +62,10 @@ public ASet<T> excludeAll(ASet<T> elements) {
 	
 	public abstract AHashSet<T> toCanonical();
 	
-	public <R extends ACell> ASet<R> conjAll(ACollection<R> elements) {
-		if (elements instanceof AHashSet) return includeAll((AHashSet<R>) elements);
-		@SuppressWarnings("unchecked")
-		AHashSet<R> result=(AHashSet<R>) this;
+	@SuppressWarnings("unchecked")
+	public AHashSet<T> conjAll(ACollection<? extends T> elements) {
+		if (elements instanceof AHashSet) return includeAll((AHashSet<T>)elements);
+		AHashSet<T> result=this;
 		long n=elements.count();
 		for (long i=0; i<n; i++) {
 			result=result.conj(elements.get(i));
@@ -91,8 +91,8 @@ public ASet<T> disjAll(ACollection<T> b) {
 
 	@SuppressWarnings("unchecked")
 	@Override
-	public <R extends ACell> AHashSet<R> conj(R a) {
-		return (AHashSet<R>) includeRef((Ref<T>) Ref.get(a));
+	public AHashSet<T> conj(ACell a) {
+		return includeRef(Ref.get((T)a));
 	}
 	
 	@Override
@@ -100,10 +100,9 @@ public ASet<T> exclude(ACell a) {
 		return excludeRef(Ref.get(a));
 	}
 	
-	@SuppressWarnings("unchecked")
 	@Override
-	public <R extends ACell> AHashSet<R> include(R a) {
-		return (AHashSet<R>) includeRef((Ref<T>) Ref.get(a));
+	public AHashSet<T> include(T a) {
+		return includeRef((Ref<T>) Ref.get(a));
 	}
 
 	/**
diff --git a/convex-core/src/main/java/convex/core/data/AList.java b/convex-core/src/main/java/convex/core/data/AList.java
index fa6c43508..d788c2d7d 100644
--- a/convex-core/src/main/java/convex/core/data/AList.java
+++ b/convex-core/src/main/java/convex/core/data/AList.java
@@ -45,7 +45,7 @@ public final AType getType() {
 	 * Returns a new list.
 	 */
 	@Override
-	public abstract <R extends ACell> AList<R> conj(R x);
+	public abstract AList<T> conj(ACell x);
 
 	@Override
 	public AList<T> empty() {
diff --git a/convex-core/src/main/java/convex/core/data/AMap.java b/convex-core/src/main/java/convex/core/data/AMap.java
index 446b6997d..fdc834a81 100644
--- a/convex-core/src/main/java/convex/core/data/AMap.java
+++ b/convex-core/src/main/java/convex/core/data/AMap.java
@@ -301,11 +301,10 @@ public Set<K> keySet() {
 	 * @return Updated map with the specified entry added, or null if the argument
 	 *         is not a valid map entry
 	 */
-	@SuppressWarnings("unchecked")
-	public <R extends ACell> ADataStructure<R> conj(R x) {
+	public AMap<K,V> conj(ACell x) {
 		MapEntry<K, V> me = RT.ensureMapEntry(x);
 		if (me == null) return null;
-		return (ADataStructure<R>) assocEntry(me);
+		return assocEntry(me);
 	}
 
 	/**
diff --git a/convex-core/src/main/java/convex/core/data/ASequence.java b/convex-core/src/main/java/convex/core/data/ASequence.java
index fe12761cd..30efe69db 100644
--- a/convex-core/src/main/java/convex/core/data/ASequence.java
+++ b/convex-core/src/main/java/convex/core/data/ASequence.java
@@ -231,10 +231,10 @@ public ACell[] toCellArray() {
 	 * Adds an element to the sequence in the natural position
 	 * 
 	 * @param value Value to add
-	 * @return Updated sequence
+	 * @return Updated sequence, or null if value is invalid
 	 */
 	@Override
-	public abstract <R extends ACell> ASequence<R> conj(R value);
+	public abstract ASequence<T> conj(ACell value);
 
 	/**
 	 * Produces a slice of this sequence, beginning with the specified start index and of the given length.
diff --git a/convex-core/src/main/java/convex/core/data/ASet.java b/convex-core/src/main/java/convex/core/data/ASet.java
index 194a0dfe3..f96df155b 100644
--- a/convex-core/src/main/java/convex/core/data/ASet.java
+++ b/convex-core/src/main/java/convex/core/data/ASet.java
@@ -42,7 +42,7 @@ public final byte getTag() {
 	 * @param a Value to include
 	 * @return Updated set
 	 */
-	public abstract <R extends ACell> ASet<R> include(R a);
+	public abstract ASet<T> include(T a);
 	
 	/**
 	 * Updates the set to exclude the given element
@@ -58,7 +58,7 @@ public final byte getTag() {
 	 * @param elements Elements to include
 	 * @return Updated set
 	 */
-	public abstract <R extends ACell> ASet<R> includeAll(ASet<R> elements) ;
+	public abstract ASet<T> includeAll(ASet<? extends T> elements) ;
 	
 	/**
 	 * Updates the set to exclude all the given elements.
@@ -69,7 +69,7 @@ public final byte getTag() {
 	public abstract ASet<T> excludeAll(ASet<T> elements) ;
 
 	@Override
-	public abstract <R extends ACell> ASet<R> conjAll(ACollection<R> xs);
+	public abstract ASet<T> conjAll(ACollection<? extends T> xs);
 
 	/**
 	 * Removes all elements from this set, returning a new set.
@@ -142,12 +142,12 @@ public final boolean contains(Object o) {
 	public abstract ASet<T> includeRef(Ref<T> ref) ;
 
 	@Override
-	public abstract <R extends ACell> ASet<R> conj(R a);
+	public abstract ASet<T> conj(ACell a);
 
 	@SuppressWarnings("unchecked")
 	@Override
 	public ASet<T> assoc(ACell key, ACell value) {
-		if (value==CVMBool.TRUE) return (ASet<T>) include(key);
+		if (value==CVMBool.TRUE) return include((T) key);
 		if (value==CVMBool.FALSE) return exclude((T) key);
 		return null;
 	}
diff --git a/convex-core/src/main/java/convex/core/data/AVector.java b/convex-core/src/main/java/convex/core/data/AVector.java
index c689133c3..812cc3b56 100644
--- a/convex-core/src/main/java/convex/core/data/AVector.java
+++ b/convex-core/src/main/java/convex/core/data/AVector.java
@@ -208,16 +208,16 @@ public AVector<T> appendAll(List<T> list) {
 
 	@SuppressWarnings("unchecked")
 	@Override
-	public final <R extends ACell> AVector<R> conj(R value) {
-		return (AVector<R>) append((T) value);
+	public final AVector<T> conj(ACell value) {
+		return append((T) value);
 	}
 	
 	@SuppressWarnings("unchecked")
-	public <R extends ACell> AVector<R> conjAll(ACollection<R> xs) {
+	public AVector<T> conjAll(ACollection<? extends T> xs) {
 		if (xs instanceof ASequence) {
-			return (AVector<R>) concat((ASequence<T>)xs);
+			return concat((ASequence<T>)xs);
 		}
-		return (AVector<R>) concat(Vectors.create(xs));
+		return concat(Vectors.create(xs));
 	}
 
 	@Override
diff --git a/convex-core/src/main/java/convex/core/data/List.java b/convex-core/src/main/java/convex/core/data/List.java
index a5ea85dfc..486496f8c 100644
--- a/convex-core/src/main/java/convex/core/data/List.java
+++ b/convex-core/src/main/java/convex/core/data/List.java
@@ -305,8 +305,8 @@ public int estimatedEncodingSize() {
 	 * @return Updated list
 	 */
 	@Override
-	public <R extends ACell> List<R> conj(R value) {
-		return new List<R>((AVector<R>) data.conj(value));
+	public List<T> conj(ACell value) {
+		return new List<T>(data.conj(value));
 	}
 	
 	@Override
@@ -314,7 +314,7 @@ public AList<T> cons(T x) {
 		return new List<T>((AVector<T>) data.conj(x));
 	}
 	
-	public <R extends ACell> List<R> conjAll(ACollection<R> xs) {
+	public List<T> conjAll(ACollection<? extends T> xs) {
 		return reverse(data.conjAll(xs));
 	}
 
diff --git a/convex-core/src/main/java/convex/core/data/Sets.java b/convex-core/src/main/java/convex/core/data/Sets.java
index 5863be821..54c185163 100644
--- a/convex-core/src/main/java/convex/core/data/Sets.java
+++ b/convex-core/src/main/java/convex/core/data/Sets.java
@@ -32,7 +32,6 @@ public static <T extends ACell> Ref<SetLeaf<T>> emptyRef() {
 		return (Ref)EMPTY_REF;
 	}
 
-	@SuppressWarnings("unchecked")
 	@SafeVarargs
 	public static <T extends ACell> ASet<T> of(Object... elements) {
 		int n=elements.length;
@@ -49,7 +48,7 @@ public static <T extends ACell> ASet<T> of(ACell... elements) {
 		int n=elements.length;
 		ASet<T> result=empty();
 		for (int i=0; i<n; i++) {
-			result=(ASet<T>) result.conj(elements[i]);
+			result=(ASet<T>) result.conj((T) elements[i]);
 		}
 		return result;
  	}
@@ -95,7 +94,7 @@ public static <T extends ACell> ASet<T> fromCollection(Collection<T> source) {
 	@SuppressWarnings("unchecked")
 	private static <T extends ACell> ASet<T> fromCollection(ACountable<T> source) {
 		long n=source.count();
-		ASet<?> set=EMPTY;
+		ASet<T> set=EMPTY;
 		for (long i=0; i<n; i++) {
 			set=set.include(source.get(i));
 		}
diff --git a/convex-core/src/main/java/convex/core/data/impl/KeySet.java b/convex-core/src/main/java/convex/core/data/impl/KeySet.java
index a1c1e92f3..bcab6c59f 100644
--- a/convex-core/src/main/java/convex/core/data/impl/KeySet.java
+++ b/convex-core/src/main/java/convex/core/data/impl/KeySet.java
@@ -28,22 +28,21 @@ public int estimatedEncodingSize() {
 	}
 
 	@Override
-	public <R extends ACell> ASet<R> include(R a) {
+	public ASet<K> include(K a) {
 		return getCanonicalSet().include(a);
 	}
 
-	protected ASet<? super K> getCanonicalSet() {
+	protected ASet<K> getCanonicalSet() {
 		return getCanonical();
 	}
 
-	@SuppressWarnings("unchecked")
 	@Override
 	public ASet<K> exclude(ACell a) {
 		return (ASet<K>) getCanonicalSet().exclude(a);
 	}
 
 	@Override
-	public <R extends ACell> ASet<R> includeAll(ASet<R> elements) {
+	public ASet<K> includeAll(ASet<? extends K> elements) {
 		return getCanonicalSet().includeAll(elements);
 	}
 
@@ -54,7 +53,7 @@ public ASet<K> excludeAll(ASet<K> elements) {
 	}
 
 	@Override
-	public <R extends ACell> ASet<R> conjAll(ACollection<R> xs) {
+	public ASet<K> conjAll(ACollection<? extends K> xs) {
 		return getCanonicalSet().conjAll(xs);
 	}
 
@@ -82,7 +81,7 @@ public ASet<K> includeRef(Ref<K> ref) {
 	}
 
 	@Override
-	public <R extends ACell> ASet<R> conj(R a) {
+	public ASet<K> conj(ACell a) {
 		return getCanonicalSet().conj(a);
 	}
 
@@ -104,7 +103,6 @@ public boolean containsAll(ASet<?> b) {
 		return getCanonicalSet().containsAll(b);
 	}
 
-	@SuppressWarnings("unchecked")
 	@Override
 	public ASet<K> slice(long start, long end) {
 		return (ASet<K>) getCanonicalSet().slice(start,end);
diff --git a/convex-core/src/test/java/convex/core/data/AdversarialDataTest.java b/convex-core/src/test/java/convex/core/data/AdversarialDataTest.java
index abccf6917..cb9e22df6 100644
--- a/convex-core/src/test/java/convex/core/data/AdversarialDataTest.java
+++ b/convex-core/src/test/java/convex/core/data/AdversarialDataTest.java
@@ -126,7 +126,7 @@ public class AdversarialDataTest {
 		
 		// Inserting non-CVM values into existing valid sets
 		invalidTest(Sets.of(1,2,3,4).include(NON_CVM));
-		invalidTest(Samples.LONG_SET_100.include(NON_CVM));
+		invalidTest(Samples.LONG_SET_100.conj(NON_CVM));
 	}
 	
 	@Test public void testBadKeywords() {