diff --git a/accord-core/src/main/java/accord/api/Key.java b/accord-core/src/main/java/accord/api/Key.java
index 1504b406c2..99804b70cc 100644
--- a/accord-core/src/main/java/accord/api/Key.java
+++ b/accord-core/src/main/java/accord/api/Key.java
@@ -21,6 +21,7 @@
 import accord.primitives.Range;
 import accord.primitives.RoutableKey;
 import accord.primitives.Seekable;
+import accord.utils.Invariants;
 
 /**
  * A key we can find in both the cluster and on disk
@@ -31,7 +32,11 @@ public interface Key extends Seekable, RoutableKey
     default Key asKey() { return this; }
 
     @Override
-    default Key slice(Range range) { return this; }
+    default Key slice(Range range)
+    {
+        Invariants.checkArgument(range.contains(this));
+        return this;
+    }
 
     @Override
     default Range asRange() { throw new UnsupportedOperationException(); }
diff --git a/accord-core/src/main/java/accord/api/Read.java b/accord-core/src/main/java/accord/api/Read.java
index c2952263ca..4f58007fc1 100644
--- a/accord-core/src/main/java/accord/api/Read.java
+++ b/accord-core/src/main/java/accord/api/Read.java
@@ -31,8 +31,26 @@
  */
 public interface Read
 {
+    /**
+     * Returns the scope of the transaction, that is, the keys or ranges that will be read
+     * // TODO maybe this method should be renamed to readScope, or just scope, or something else which would not mention keys as it can be ranges as well?
+     */
     Seekables<?, ?> keys();
+
+    /**
+     * The method is called when Accord reads data.
+     *
+     * @param key denotes which data to read; it is guaranteed that the key passed there is one of the items covered by {@link #keys()}.
+     */
     AsyncChain<Data> read(Seekable key, Txn.Kind kind, SafeCommandStore commandStore, Timestamp executeAt, DataStore store);
+
+    /**
+     * Returns a new read operation whose scope is an intersection of {@link #keys()} and the provided ranges.
+     */
     Read slice(Ranges ranges);
+
+    /**
+     * Returns a new read operation whose scope is a union of the scopes of this and the provided read operations.
+     */
     Read merge(Read other);
 }
diff --git a/accord-core/src/main/java/accord/api/Update.java b/accord-core/src/main/java/accord/api/Update.java
index b3eb387553..cba9417273 100644
--- a/accord-core/src/main/java/accord/api/Update.java
+++ b/accord-core/src/main/java/accord/api/Update.java
@@ -19,21 +19,34 @@
 package accord.api;
 
 import accord.primitives.Ranges;
-import accord.primitives.Keys;
 import accord.primitives.Seekables;
 
 import javax.annotation.Nullable;
 
 /**
  * A client-defined update operation (the write equivalent of a query).
- * Takes as input the data returned by {@code Read}, and returns a {@code Write}
- * representing new information to distributed to each shard's stores.
  */
 public interface Update
 {
+    /**
+     * Returns the scope of the transaction, that is, the keys or ranges that will be written
+     */
+    //TODO maybe this method should be renamed to updateScope, or just scope, or something else which would not mention keys as it can be ranges as well?
     Seekables<?, ?> keys();
-    // null is provided only if nothing was read
+
+    /**
+     * Takes as input the data returned by {@link Read}, and returns a {@link Write} representing new information
+     * to be distributed to each shard's stores. Accepts {@code null} if nothing was read.
+     */
     Write apply(@Nullable Data data);
+
+    /**
+     * Returns a new update operation whose scope is an intersection of {@link #keys()} and the provided ranges.
+     */
     Update slice(Ranges ranges);
+
+    /**
+     * Returns a new update operation whose scope is a union of the scopes of this and the provided update operations.
+     */
     Update merge(Update other);
 }
diff --git a/accord-core/src/main/java/accord/primitives/AbstractKeys.java b/accord-core/src/main/java/accord/primitives/AbstractKeys.java
index 6e4c716c5c..72bedaac72 100644
--- a/accord-core/src/main/java/accord/primitives/AbstractKeys.java
+++ b/accord-core/src/main/java/accord/primitives/AbstractKeys.java
@@ -35,7 +35,7 @@
 
 @SuppressWarnings("rawtypes")
 // TODO (desired, efficiency): check that foldl call-sites are inlined and optimised by HotSpot
-public abstract class AbstractKeys<K extends RoutableKey, KS extends Routables<K, ?>> implements Iterable<K>, Routables<K, KS>
+public abstract class AbstractKeys<K extends RoutableKey, KS extends Routables<K, KS>> implements Iterable<K>, Routables<K, KS>
 {
     final K[] keys;
 
diff --git a/accord-core/src/main/java/accord/primitives/AbstractRanges.java b/accord-core/src/main/java/accord/primitives/AbstractRanges.java
index 0fa91858ee..8ed332be4d 100644
--- a/accord-core/src/main/java/accord/primitives/AbstractRanges.java
+++ b/accord-core/src/main/java/accord/primitives/AbstractRanges.java
@@ -33,7 +33,7 @@
 import static accord.utils.SortedArrays.Search.FAST;
 import static accord.utils.SortedArrays.swapHighLow32b;
 
-public abstract class AbstractRanges<RS extends Routables<Range, ?>> implements Iterable<Range>, Routables<Range, RS>
+public abstract class AbstractRanges<RS extends Routables<Range, RS>> implements Iterable<Range>, Routables<Range, RS>
 {
     static final Range[] NO_RANGES = new Range[0];
 
@@ -41,6 +41,13 @@ public abstract class AbstractRanges<RS extends Routables<Range, ?>> implements
 
     AbstractRanges(@Nonnull Range[] ranges)
     {
+        if (ranges.length > 0)
+        {
+            // check that ranges are of the same type
+            for (int i = 1; i < ranges.length; i++)
+                ranges[0].checkRangeType(ranges[i]);
+        }
+
         // TODO (simple, validation): check ranges are non-overlapping (or make sure it's safe for all methods that they aren't)
         this.ranges = Invariants.nonNull(ranges);
     }
@@ -110,6 +117,7 @@ public boolean intersectsAll(AbstractRanges<?> that)
     {
         if (this.isEmpty()) return that.isEmpty();
         if (that.isEmpty()) return true;
+        this.ranges[0].checkRangeType(that.ranges[0]);
         return Routables.rangeFoldl(that, this, (p, v, from, to) -> v + (to - from), 0, 0, 0) == that.size();
     }
 
diff --git a/accord-core/src/main/java/accord/primitives/AbstractUnseekableKeys.java b/accord-core/src/main/java/accord/primitives/AbstractUnseekableKeys.java
index 214190e876..b9386fcf9c 100644
--- a/accord-core/src/main/java/accord/primitives/AbstractUnseekableKeys.java
+++ b/accord-core/src/main/java/accord/primitives/AbstractUnseekableKeys.java
@@ -23,7 +23,7 @@
 import java.util.Arrays;
 
 // TODO: do we need this class?
-public abstract class AbstractUnseekableKeys<KS extends Unseekables<RoutingKey, ?>> extends AbstractKeys<RoutingKey, KS> implements Iterable<RoutingKey>, Unseekables<RoutingKey, KS>
+public abstract class AbstractUnseekableKeys<KS extends Unseekables<RoutingKey, KS>> extends AbstractKeys<RoutingKey, KS> implements Iterable<RoutingKey>, Unseekables<RoutingKey, KS>
 {
     AbstractUnseekableKeys(RoutingKey[] keys)
     {
diff --git a/accord-core/src/main/java/accord/primitives/FullRoute.java b/accord-core/src/main/java/accord/primitives/FullRoute.java
index a9acba1048..40590b982b 100644
--- a/accord-core/src/main/java/accord/primitives/FullRoute.java
+++ b/accord-core/src/main/java/accord/primitives/FullRoute.java
@@ -18,7 +18,7 @@
 
 package accord.primitives;
 
-public interface FullRoute<T extends Unseekable> extends Route<T>, Unseekables<T, Route<T>>
+public interface FullRoute<T extends Unseekable> extends Route<T>
 {
     @Override default FullRoute<T> union(Route<T> route) { return this; }
     @Override default Ranges sliceCovering(Ranges newRanges, Slice slice) { return newRanges; }
diff --git a/accord-core/src/main/java/accord/primitives/Range.java b/accord-core/src/main/java/accord/primitives/Range.java
index db6c3aa021..3edcfc16e3 100644
--- a/accord-core/src/main/java/accord/primitives/Range.java
+++ b/accord-core/src/main/java/accord/primitives/Range.java
@@ -30,7 +30,7 @@
 import static accord.utils.SortedArrays.Search.FAST;
 
 /**
- * A range of keys
+ * A range of keys.
  */
 public abstract class Range implements Comparable<RoutableKey>, Unseekable, Seekable
 {
@@ -52,13 +52,13 @@ public int compareTo(RoutableKey key)
         }
 
         @Override
-        public boolean startInclusive()
+        public final boolean startInclusive()
         {
             return false;
         }
 
         @Override
-        public boolean endInclusive()
+        public final boolean endInclusive()
         {
             return true;
         }
@@ -94,13 +94,13 @@ public int compareTo(RoutableKey key)
         }
 
         @Override
-        public boolean startInclusive()
+        public final boolean startInclusive()
         {
             return true;
         }
 
         @Override
-        public boolean endInclusive()
+        public final boolean endInclusive()
         {
             return false;
         }
@@ -244,8 +244,7 @@ public boolean contains(RoutableKey key)
      */
     public int compareIntersecting(Range that)
     {
-        if (that.getClass() != this.getClass())
-            throw new IllegalArgumentException("Cannot mix Range of different types");
+        checkRangeType(that);
         if (this.start.compareTo(that.end) >= 0)
             return 1;
         if (this.end.compareTo(that.start) <= 0)
@@ -258,8 +257,7 @@ public int compareIntersecting(Range that)
      */
     public int compare(Range that)
     {
-        if (that.getClass() != this.getClass())
-            throw new IllegalArgumentException("Cannot mix Range of different types");
+        checkRangeType(that);
         int c = this.start.compareTo(that.start);
         if (c == 0) c = this.end.compareTo(that.end);
         return c;
@@ -272,10 +270,9 @@ public boolean contains(Range that)
 
     public Range slice(Range truncateTo)
     {
-        int cs = start.compareTo(truncateTo.start);
-        int ce = end.compareTo(truncateTo.end);
-        if (cs >= 0 && ce <= 0) return this;
-        return newRange(cs >= 0 ? start : truncateTo.start, ce <= 0 ? end : truncateTo.end);
+        Range intersection = this.intersection(truncateTo);
+        Invariants.checkArgument(intersection != null);
+        return intersection;
     }
 
     public boolean intersects(AbstractKeys<?, ?> keys)
@@ -289,11 +286,20 @@ public boolean intersects(AbstractKeys<?, ?> keys)
      */
     public Range intersection(Range that)
     {
+        checkRangeType(that);
+
         if (this.compareIntersecting(that) != 0)
             return null;
 
         RoutingKey start = this.start.compareTo(that.start) > 0 ? this.start : that.start;
         RoutingKey end = this.end.compareTo(that.end) < 0 ? this.end : that.end;
+
+        if (start == this.start && end == this.end)
+            return this;
+
+        if (start == that.start && end == that.end)
+            return that;
+
         return newRange(start, end);
     }
 
@@ -349,21 +355,15 @@ public RoutingKey someIntersectingRoutingKey(Ranges ranges)
         }
     }
 
-    public static Range slice(Range bound, Range toSlice)
-    {
-        Invariants.checkArgument(bound.compareIntersecting(toSlice) == 0);
-        if (bound.contains(toSlice))
-            return toSlice;
-
-        return toSlice.newRange(
-                toSlice.start().compareTo(bound.start()) >= 0 ? toSlice.start() : bound.start(),
-                toSlice.end().compareTo(bound.end()) <= 0 ? toSlice.end() : bound.end()
-        );
-    }
-
     @Override
     public Range toUnseekable()
     {
         return this;
     }
+
+    final void checkRangeType(Range that)
+    {
+        if (that.getClass() != this.getClass())
+            throw new IllegalArgumentException(String.format("Cannot mix Range of different types (%s and %s)", this.getClass().getSimpleName(), that.getClass().getSimpleName()));
+    }
 }
diff --git a/accord-core/src/main/java/accord/primitives/Routables.java b/accord-core/src/main/java/accord/primitives/Routables.java
index 627982191e..987c420fc0 100644
--- a/accord-core/src/main/java/accord/primitives/Routables.java
+++ b/accord-core/src/main/java/accord/primitives/Routables.java
@@ -24,18 +24,15 @@
 import accord.utils.IndexedFoldToLong;
 import accord.utils.IndexedRangeFoldToLong;
 import accord.utils.SortedArrays;
-import net.nicoulaj.compilecommand.annotations.Inline;
 
-import java.util.function.BiFunction;
-import java.util.function.Function;
+import net.nicoulaj.compilecommand.annotations.Inline;
 
-import static accord.primitives.Routables.Slice.Overlapping;
 import static accord.utils.SortedArrays.Search.FLOOR;
 
 /**
  * A collection of either Seekable or Unseekable
  */
-public interface Routables<K extends Routable, U extends Routables<K, ?>> extends Iterable<K>
+public interface Routables<K extends Routable, U extends Routables<K, U>> extends Iterable<K>
 {
     enum Slice
     {
diff --git a/accord-core/src/main/java/accord/primitives/RoutingKeys.java b/accord-core/src/main/java/accord/primitives/RoutingKeys.java
index 3db75ab3e6..bff7ad6001 100644
--- a/accord-core/src/main/java/accord/primitives/RoutingKeys.java
+++ b/accord-core/src/main/java/accord/primitives/RoutingKeys.java
@@ -23,7 +23,7 @@
 
 import static accord.utils.ArrayBuffers.cachedRoutingKeys;
 
-public class RoutingKeys extends AbstractUnseekableKeys<AbstractUnseekableKeys<?>> implements Unseekables<RoutingKey, AbstractUnseekableKeys<?>>
+public class RoutingKeys extends AbstractUnseekableKeys<RoutingKeys>
 {
     public static class SerializationSupport
     {
diff --git a/accord-core/src/main/java/accord/primitives/Seekable.java b/accord-core/src/main/java/accord/primitives/Seekable.java
index a3cec1f642..90a46318ae 100644
--- a/accord-core/src/main/java/accord/primitives/Seekable.java
+++ b/accord-core/src/main/java/accord/primitives/Seekable.java
@@ -21,11 +21,24 @@
 import accord.api.Key;
 
 /**
- * Something that can be found within the cluster AND found on disk, queried and returned
+ * Something that can be found within the cluster AND found on disk, queried and returned - in particular, it includes
+ * enough information to be found on disk (in constrast to {@link Unseekable}.
  */
 public interface Seekable extends Routable
 {
+    /**
+     * If this is a key, it will return itself, otherwise it throw an exception
+     */
     Key asKey();
+
+    /**
+     * If this is a range, it will return itself, otherwise it throw an exception
+     */
     Range asRange();
+
+    /**
+     * Returns a {@link Seekable} of the same type as this one truncated to the given range (intersection).
+     * If the provided range does not intersect with this {@link Seekable}, an exception is thrown.
+     */
     Seekable slice(Range range);
 }
diff --git a/accord-core/src/main/java/accord/primitives/Seekables.java b/accord-core/src/main/java/accord/primitives/Seekables.java
index 3ae8448b57..fe4ed4d87d 100644
--- a/accord-core/src/main/java/accord/primitives/Seekables.java
+++ b/accord-core/src/main/java/accord/primitives/Seekables.java
@@ -25,7 +25,7 @@
 /**
  * Either a Route or a collection of Routable
  */
-public interface Seekables<K extends Seekable, U extends Seekables<K, ?>> extends Routables<K, U>
+public interface Seekables<K extends Seekable, U extends Seekables<K, U>> extends Routables<K, U>
 {
     @Override
     default U slice(Ranges ranges) { return slice(ranges, Overlapping); }
diff --git a/accord-core/src/main/java/accord/primitives/Unseekable.java b/accord-core/src/main/java/accord/primitives/Unseekable.java
index 2c40e95d64..a86b91527d 100644
--- a/accord-core/src/main/java/accord/primitives/Unseekable.java
+++ b/accord-core/src/main/java/accord/primitives/Unseekable.java
@@ -19,7 +19,10 @@
 package accord.primitives;
 
 /**
- * Something that can only be routed, i.e. is NOT a Seekable.
+ * Something that can only be routed.
+ * In particular, it purposely does not contain enough information to found it on disk (in contrast to {@link Seekable}).
+ * Those two interfaces were created to explicitly distinguish what information it is intended to be serialized when
+ * exchanging data between nodes. {@link Seekable} contains more information, but it is not always necessary to send it.
  */
 public interface Unseekable extends Routable
 {
diff --git a/accord-core/src/main/java/accord/primitives/Unseekables.java b/accord-core/src/main/java/accord/primitives/Unseekables.java
index 5294555c4d..4f02b50236 100644
--- a/accord-core/src/main/java/accord/primitives/Unseekables.java
+++ b/accord-core/src/main/java/accord/primitives/Unseekables.java
@@ -23,7 +23,7 @@
 /**
  * Either a Route or a simple collection of keys or ranges
  */
-public interface Unseekables<K extends Unseekable, U extends Unseekables<K, ?>> extends Iterable<K>, Routables<K, U>
+public interface Unseekables<K extends Unseekable, U extends Unseekables<K, U>> extends Iterable<K>, Routables<K, U>
 {
     enum UnseekablesKind
     {