diff --git a/.gitignore b/.gitignore
index 724d50a..31e9878 100644
--- a/.gitignore
+++ b/.gitignore
@@ -24,7 +24,9 @@ hs_err_pid*
 # Custom Stuff
 # Gradle
 .gradle/*
-build/*
+**/build/*
+**/out/**
+**/.DS_Store
 
 # IntelliJ
 .idea/*
diff --git a/core/src/main/java/org/nwapw/abacus/number/NumberInterface.java b/core/src/main/java/org/nwapw/abacus/number/NumberInterface.java
index 8727425..e37c4fb 100755
--- a/core/src/main/java/org/nwapw/abacus/number/NumberInterface.java
+++ b/core/src/main/java/org/nwapw/abacus/number/NumberInterface.java
@@ -5,7 +5,7 @@ import org.nwapw.abacus.exception.ComputationInterruptedException;
 /**
  * An interface used to represent a number.
  */
-public abstract class NumberInterface {
+public abstract class NumberInterface implements Comparable<NumberInterface> {
 
     /**
      * Check if the thread was interrupted and
@@ -158,14 +158,6 @@ public abstract class NumberInterface {
         return intPowInternal(exponent);
     }
 
-    /**
-     * Compares this number to another.
-     *
-     * @param number the number to compare to.
-     * @return same as Integer.compare();
-     */
-    public abstract int compareTo(NumberInterface number);
-
     /**
      * Same as Math.signum().
      *
diff --git a/core/src/main/kotlin/org/nwapw/abacus/Abacus.kt b/core/src/main/kotlin/org/nwapw/abacus/Abacus.kt
index 0363646..4272aa8 100644
--- a/core/src/main/kotlin/org/nwapw/abacus/Abacus.kt
+++ b/core/src/main/kotlin/org/nwapw/abacus/Abacus.kt
@@ -68,6 +68,7 @@ class Abacus(val configuration: Configuration) {
         pluginManager.reload()
         with(mutableContext) {
             numberImplementation = pluginManager.numberImplementationFor(configuration.numberImplementation)
+                    ?: StandardPlugin.IMPLEMENTATION_NAIVE
             clearVariables()
             clearDefinitions()
         }
@@ -87,7 +88,7 @@ class Abacus(val configuration: Configuration) {
      * @param input the input string to parse
      * @return the resulting tree, null if the tree builder or the produced tree are null.
      */
-    fun parseString(input: String): TreeNode? = treeBuilder.fromString(input)
+    fun parseString(input: String): TreeNode = treeBuilder.fromString(input)
     /**
      * Evaluates the given tree.
      *