diff --git a/.gitignore b/.gitignore
index 77b3a40..a007f0d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -36,6 +36,8 @@ gradle-app.setting
 *.tar.gz
 *.rar
 
+*.minisig
+
 # virtual machine crash logs, see http://www.java.com/en/download/help/error_hotspot.xml
 hs_err_pid*
 replay_pid*
diff --git a/app/src/main/java/hatelace/Address.java b/app/src/main/java/hatelace/Address.java
index fb4d249..f914865 100644
--- a/app/src/main/java/hatelace/Address.java
+++ b/app/src/main/java/hatelace/Address.java
@@ -1,6 +1,6 @@
 package hatelace;
 
-public class Address {
+public class Address implements Operand {
     int address;
 
     public Address(int address) {
@@ -14,4 +14,8 @@ public class Address {
     public String toString() {
         return Integer.toString(address);
     }
+
+    public Word getWord(Memory memory) {
+        return memory.read(this);
+    }
 }
diff --git a/app/src/main/java/hatelace/Operand.java b/app/src/main/java/hatelace/Operand.java
new file mode 100644
index 0000000..bcdc6be
--- /dev/null
+++ b/app/src/main/java/hatelace/Operand.java
@@ -0,0 +1,5 @@
+package hatelace;
+
+public interface Operand {
+    Word getWord(Memory memory);
+}
diff --git a/app/src/main/java/hatelace/Word.java b/app/src/main/java/hatelace/Word.java
index db74dbc..b0bbb17 100644
--- a/app/src/main/java/hatelace/Word.java
+++ b/app/src/main/java/hatelace/Word.java
@@ -1,6 +1,6 @@
 package hatelace;
 
-public abstract class Word {
+public abstract class Word implements Operand {
     public abstract <T> T getValue();
     public abstract Word add(Word other);
     public abstract Word subtract(Word other);
diff --git a/app/src/main/java/hatelace/instructions/Add.java b/app/src/main/java/hatelace/instructions/Add.java
index fc5c2ab..1b88504 100644
--- a/app/src/main/java/hatelace/instructions/Add.java
+++ b/app/src/main/java/hatelace/instructions/Add.java
@@ -3,19 +3,18 @@ package hatelace.instructions;
 import hatelace.*;
 
 public class Add extends Instruction {
-    private Address src;
-    private Word imm;
     private Address dest;
+    private Operand o1, o2;
 
     /** Add immediate value to memory address. */
-    public Add(Address src, Word imm, Address dest) {
-        this.src = src;
-        this.imm = imm;
+    public Add(Operand o1, Operand o2, Address dest) {
+        this.o1 = o1;
+        this.o2 = o2;
         this.dest = dest;
     }
 
     public void execute(Memory memory, ProgramCounter PC) {
-        memory.write(this.dest, memory.read(this.src).add(this.imm));
+        memory.write(this.dest, this.o1.getWord(memory).add(this.o2.getWord(memory)));
         PC.incPC();
     }
 
@@ -24,10 +23,10 @@ public class Add extends Instruction {
     }
 
     public String toString() {
-        return String.format("%s [%s] %s [%s]", this.opcode(), this.src, this.imm, this.dest);
+        return String.format("%s [%s] %s [%s]", this.opcode(), this.o1, this.o2, this.dest);
     }
 
     protected Object[] operands() {
-        return new Object[] { this.src, this.imm, this.dest };
+        return new Object[] { this.o1, this.o2, this.dest };
     }
 }
diff --git a/app/src/main/java/hatelace/instructions/Copy.java b/app/src/main/java/hatelace/instructions/Copy.java
index 985ce1a..a88c27e 100644
--- a/app/src/main/java/hatelace/instructions/Copy.java
+++ b/app/src/main/java/hatelace/instructions/Copy.java
@@ -3,17 +3,17 @@ package hatelace.instructions;
 import hatelace.*;
 
 public class Copy extends Instruction {
-    private Word imm;
+    private Operand src;
     private Address dest;
 
     /** Copy immediate value to memory address. */
-    public Copy(Word imm, Address dest) {
-        this.imm = imm;
+    public Copy(Operand src, Address dest) {
+        this.src = src;
         this.dest = dest;
     }
 
     public void execute(Memory memory, ProgramCounter PC) {
-        memory.write(this.dest, this.imm);
+        memory.write(this.dest, this.src.getWord(memory));
         PC.incPC();
     }
 
@@ -22,10 +22,10 @@ public class Copy extends Instruction {
     }
 
     protected Object[] operands() {
-        return new Object[] {this.imm, this.dest};
+        return new Object[] {this.src, this.dest};
     }
 
     public String toString() {
-        return String.format("%s %s [%s]", this.opcode(), this.imm, this.dest);
+        return String.format("%s %s [%s]", this.opcode(), this.src, this.dest);
     }
 }
diff --git a/app/src/main/java/hatelace/instructions/JumpEq.java b/app/src/main/java/hatelace/instructions/JumpEq.java
index f2538be..a0b27ba 100644
--- a/app/src/main/java/hatelace/instructions/JumpEq.java
+++ b/app/src/main/java/hatelace/instructions/JumpEq.java
@@ -4,18 +4,18 @@ import hatelace.*;
 
 public class JumpEq extends Instruction {
     private int index;
-    private Address src;
-    private Word imm;
+    private Operand o1;
+    private Operand o2;
 
     /** Conditional jump */
-    public JumpEq(int index, Address src, Word imm) {
+    public JumpEq(int index, Operand o1, Operand o2) {
         this.index = index;
-        this.src = src;
-        this.imm = imm;
+        this.o1 = o1;
+        this.o2 = o2;
     }
 
     public void execute(Memory memory, ProgramCounter PC) {
-        if (this.imm.equals(memory.read(this.src))) {
+        if (this.o1.getWord(memory).equals(this.o2.getWord(memory))) {
             PC.setPC(this.index);
         } else {
             PC.incPC();
@@ -27,10 +27,10 @@ public class JumpEq extends Instruction {
     }
 
     protected Object[] operands() {
-        return new Object[] {this.index, this.src, this.imm};
+        return new Object[] {this.index, this.o1, this.o2};
     }
 
     public String toString() {
-        return String.format("%s %s [%s] %s", this.opcode(), this.index, this.src, this.imm);
+        return String.format("%s %s [%s] %s", this.opcode(), this.index, this.o1, this.o2);
     }
 }
diff --git a/app/src/main/java/hatelace/instructions/Mul.java b/app/src/main/java/hatelace/instructions/Mul.java
index cd61d81..4536682 100644
--- a/app/src/main/java/hatelace/instructions/Mul.java
+++ b/app/src/main/java/hatelace/instructions/Mul.java
@@ -3,19 +3,19 @@ package hatelace.instructions;
 import hatelace.*;
 
 public class Mul extends Instruction {
-    private Address src1;
-    private Address src2;
+    private Operand o1;
+    private Operand o2;
     private Address dest;
 
     /** Multiply contents of two addresses and store the result in a third memory address. */
-    public Mul(Address src1, Address src2, Address dest) {
-        this.src1 = src1;
-        this.src2 = src2;
+    public Mul(Operand o1, Operand o2, Address dest) {
+        this.o1 = o1;
+        this.o2 = o2;
         this.dest = dest;
     }
 
     public void execute(Memory memory, ProgramCounter PC) {
-        memory.write(this.dest, memory.read(this.src1).multiply(memory.read(this.src2)));
+        memory.write(this.dest, this.o1.getWord(memory).multiply(this.o2.getWord(memory)));
         PC.incPC();
     }
 
@@ -24,10 +24,10 @@ public class Mul extends Instruction {
     }
 
     protected Object[] operands() {
-        return new Object[] { this.src1, this.src2, this.dest };
+        return new Object[] { this.o1, this.o2, this.dest };
     }
 
     public String toString() {
-        return String.format("%s [%s] [%s] [%s]", this.opcode(), this.src1, this.src2, this.dest);
+        return String.format("%s [%s] [%s] [%s]", this.opcode(), this.o1, this.o2, this.dest);
     }
 }
diff --git a/app/src/main/java/hatelace/memtypes/IntWord.java b/app/src/main/java/hatelace/memtypes/IntWord.java
index 75c00a8..ba8402d 100644
--- a/app/src/main/java/hatelace/memtypes/IntWord.java
+++ b/app/src/main/java/hatelace/memtypes/IntWord.java
@@ -1,5 +1,6 @@
 package hatelace.memtypes;
 
+import hatelace.Memory;
 import hatelace.Word;
 
 public class IntWord extends Word {
@@ -15,6 +16,11 @@ public class IntWord extends Word {
         return value;
     }
 
+    @Override
+    public Word getWord(Memory memory) {
+        return this;
+    }
+
     public Word add(Word other) {
         return new IntWord(value + (Integer) other.getValue());
     }
diff --git a/app/src/main/java/hatelace/memtypes/LongWord.java b/app/src/main/java/hatelace/memtypes/LongWord.java
index f01ace2..272ffd5 100644
--- a/app/src/main/java/hatelace/memtypes/LongWord.java
+++ b/app/src/main/java/hatelace/memtypes/LongWord.java
@@ -1,5 +1,6 @@
 package hatelace.memtypes;
 
+import hatelace.Memory;
 import hatelace.Word;
 
 public class LongWord extends Word {
@@ -15,6 +16,11 @@ public class LongWord extends Word {
         return value;
     }
 
+    @Override
+    public Word getWord(Memory memory) {
+        return this;
+    }
+
     public Word add(Word other) {
         return new LongWord(value + (Long) other.getValue());
     }