diff --git a/README.md b/README.md
index cf655191f..9737a2f04 100644
--- a/README.md
+++ b/README.md
@@ -165,7 +165,7 @@ This is how you iterate:
                   x.times x
               x.write
                 x.plus 1
-    TRUE
+    true
 ```
 
 This code will print this:
diff --git a/eo-maven-plugin/src/it/duplicate_classes/src/test/eo/equality-test.eo b/eo-maven-plugin/src/it/duplicate_classes/src/test/eo/equality-test.eo
index 996155de4..021666e89 100644
--- a/eo-maven-plugin/src/it/duplicate_classes/src/test/eo/equality-test.eo
+++ b/eo-maven-plugin/src/it/duplicate_classes/src/test/eo/equality-test.eo
@@ -29,4 +29,4 @@
 [] > ensures-equality
   eq. > @
     equality
-    TRUE
\ No newline at end of file
+    true
\ No newline at end of file
diff --git a/eo-maven-plugin/src/it/fibonacci/src/main/eo/org/eolang/examples/longname.eo b/eo-maven-plugin/src/it/fibonacci/src/main/eo/org/eolang/examples/longname.eo
index 3656e5728..697ae62cf 100644
--- a/eo-maven-plugin/src/it/fibonacci/src/main/eo/org/eolang/examples/longname.eo
+++ b/eo-maven-plugin/src/it/fibonacci/src/main/eo/org/eolang/examples/longname.eo
@@ -81,4 +81,4 @@
                                                                               [] > blah38
                                                                                 blah39 > @
                                                                                 [] > blah39
-                                                                                  TRUE > @
+                                                                                  true > @
diff --git a/eo-parser/src/main/antlr4/org/eolang/parser/Eo.g4 b/eo-parser/src/main/antlr4/org/eolang/parser/Eo.g4
index f78404f27..3edb53c94 100644
--- a/eo-parser/src/main/antlr4/org/eolang/parser/Eo.g4
+++ b/eo-parser/src/main/antlr4/org/eolang/parser/Eo.g4
@@ -541,7 +541,6 @@ as  : COLON (NAME | INT)
 
 // Data
 data: BYTES
-    | BOOL
     | TEXT
     | STRING
     | INT
@@ -638,10 +637,6 @@ BYTES
     | LINE_BYTES (MINUS EOL LINE_BYTES)*
     ;
 
-BOOL: 'TRUE'
-    | 'FALSE'
-    ;
-
 fragment ESCAPE_SEQUENCE
     : '\\' [btnfr"'\\]
     | '\\' ([0-3]? [0-7])? [0-7]
diff --git a/eo-parser/src/main/java/org/eolang/parser/XeEoListener.java b/eo-parser/src/main/java/org/eolang/parser/XeEoListener.java
index 89db8cee4..69dd90b91 100644
--- a/eo-parser/src/main/java/org/eolang/parser/XeEoListener.java
+++ b/eo-parser/src/main/java/org/eolang/parser/XeEoListener.java
@@ -1225,14 +1225,6 @@ public final class XeEoListener implements EoListener, Iterable<Directive> {
             type = "bytes";
             base = "bytes";
             data = text.replaceAll("\\s+", "").replace("-", " ").trim();
-        } else if (ctx.BOOL() != null) {
-            type = "bytes";
-            base = "bool";
-            if (Boolean.parseBoolean(text)) {
-                data = XeEoListener.bytesToHex((byte) 0x01);
-            } else {
-                data = XeEoListener.bytesToHex((byte) 0x00);
-            }
         } else if (ctx.FLOAT() != null) {
             type = "bytes";
             base = "float";
diff --git a/eo-runtime/src/main/eo/org/eolang/switch.eo b/eo-runtime/src/main/eo/org/eolang/switch.eo
index 0a5c45ce5..3ea05f5d2 100644
--- a/eo-runtime/src/main/eo/org/eolang/switch.eo
+++ b/eo-runtime/src/main/eo/org/eolang/switch.eo
@@ -29,12 +29,12 @@
 # Allow to choose right options according to cases conditions.
 # Parameter cases is the array of two dimensional array, which
 # consist of condition bool value and expected value, if this
-# condition is TRUE.
+# condition is true.
 # e.g.
 # switch
 #   *
 #     *
-#       TRUE
+#       true
 #       "this value will be returned"
 #     *
 #       FALSE
@@ -45,12 +45,12 @@
   cases.length > len!
 
   # Take case by given index.
-  # If case key is TRUE, return case value.
+  # If case key is true, return case value.
   # Otherwise take next case.
   [index] > case-at
     if > @
       index.eq ^.len
-      TRUE
+      true
       if
         at.
           ^.cases.at index > case
diff --git a/eo-runtime/src/main/java/EOorg/EOeolang/EOif.java b/eo-runtime/src/main/java/EOorg/EOeolang/EOif.java
deleted file mode 100644
index 58138dd69..000000000
--- a/eo-runtime/src/main/java/EOorg/EOeolang/EOif.java
+++ /dev/null
@@ -1,68 +0,0 @@
-/*
- * The MIT License (MIT)
- *
- * Copyright (c) 2016-2024 Objectionary.com
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included
- * in all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
- * SOFTWARE.
- */
-
-/*
- * @checkstyle PackageNameCheck (4 lines)
- */
-package EOorg.EOeolang;
-
-import org.eolang.AtVoid;
-import org.eolang.Atom;
-import org.eolang.Param;
-import org.eolang.PhDefault;
-import org.eolang.Phi;
-import org.eolang.Versionized;
-import org.eolang.XmirObject;
-
-/**
- * IF.
- *
- * @since 0.36.0
- * @checkstyle TypeNameCheck (5 lines)
- */
-@Versionized
-@XmirObject(oname = "if")
-public final class EOif extends PhDefault implements Atom {
-    /**
-     * Ctor.
-     * @param sigma Sigma
-     */
-    public EOif(final Phi sigma) {
-        super(sigma);
-        this.add("condition", new AtVoid("condition"));
-        this.add("left", new AtVoid("left"));
-        this.add("right", new AtVoid("right"));
-    }
-
-    @Override
-    public Phi lambda() {
-        final Phi out;
-        if (new Param(this, "condition").strong(Boolean.class)) {
-            out = this.take("left");
-        } else {
-            out = this.take("right");
-        }
-        return out;
-    }
-}
diff --git a/eo-runtime/src/main/java/org/eolang/Data.java b/eo-runtime/src/main/java/org/eolang/Data.java
index 73466df06..b71e0414b 100644
--- a/eo-runtime/src/main/java/org/eolang/Data.java
+++ b/eo-runtime/src/main/java/org/eolang/Data.java
@@ -146,46 +146,37 @@ public interface Data {
          */
         private static Phi toPhi(final Object obj) {
             final Phi phi;
-            final byte[] bytes;
-            final boolean delta;
             final Phi eolang = Phi.Φ.take("org").take("eolang");
             if (obj instanceof Boolean) {
-                phi = eolang.take("bool").copy();
-                delta = false;
                 if (obj.equals(true)) {
-                    bytes = new byte[] {0x01};
+                    phi = eolang.take("true");
                 } else {
-                    bytes = new byte[] {0x00};
+                    phi = eolang.take("false");
                 }
             } else if (obj instanceof byte[]) {
                 phi = eolang.take("bytes").copy();
-                delta = true;
-                bytes = (byte[]) obj;
-            } else if (obj instanceof Long) {
-                phi = eolang.take("int").copy();
-                delta = false;
-                bytes = new BytesOf((Long) obj).take();
-            } else if (obj instanceof String) {
-                phi = eolang.take("string").copy();
-                delta = false;
-                bytes = Data.ToPhi.unescapeJavaString(
-                    (String) obj
-                ).getBytes(StandardCharsets.UTF_8);
-            } else if (obj instanceof Double) {
-                phi = eolang.take("float").copy();
-                delta = false;
-                bytes = new BytesOf((Double) obj).take();
-            } else {
-                throw new IllegalArgumentException(
-                    String.format(
-                        "Unknown type of data: %s",
-                        obj.getClass().getCanonicalName()
-                    )
-                );
-            }
-            if (delta) {
-                phi.attach(bytes);
+                phi.attach((byte[]) obj);
             } else {
+                final byte[] bytes;
+                if (obj instanceof Long) {
+                    phi = eolang.take("int").copy();
+                    bytes = new BytesOf((Long) obj).take();
+                } else if (obj instanceof String) {
+                    phi = eolang.take("string").copy();
+                    bytes = Data.ToPhi.unescapeJavaString(
+                        (String) obj
+                    ).getBytes(StandardCharsets.UTF_8);
+                } else if (obj instanceof Double) {
+                    phi = eolang.take("float").copy();
+                    bytes = new BytesOf((Double) obj).take();
+                } else {
+                    throw new IllegalArgumentException(
+                        String.format(
+                            "Unknown type of data: %s",
+                            obj.getClass().getCanonicalName()
+                        )
+                    );
+                }
                 final Phi bts = eolang.take("bytes").copy();
                 bts.attach(bytes);
                 phi.put(0, bts);
diff --git a/eo-runtime/src/main/java/org/eolang/Main.java b/eo-runtime/src/main/java/org/eolang/Main.java
index 05f62c794..b72d138df 100644
--- a/eo-runtime/src/main/java/org/eolang/Main.java
+++ b/eo-runtime/src/main/java/org/eolang/Main.java
@@ -134,7 +134,7 @@ public final class Main {
     /**
      * Process one option.
      * @param opt The option
-     * @return TRUE if it's time to exit
+     * @return True if it's time to exit
      * @throws IOException If fails
      */
     private static boolean parse(final String opt) throws IOException {
diff --git a/eo-runtime/src/test/eo/org/eolang/bool-tests.eo b/eo-runtime/src/test/eo/org/eolang/bool-tests.eo
index 5bc49d103..183b9c6d7 100644
--- a/eo-runtime/src/test/eo/org/eolang/bool-tests.eo
+++ b/eo-runtime/src/test/eo/org/eolang/bool-tests.eo
@@ -29,18 +29,18 @@
 # Test.
 [] > compares-two-bools
   eq. > @
-    TRUE
-    TRUE
+    true
+    true
 
 # Test.
 [] > true-as-bool
-  TRUE.as-bool > @
+  true.as-bool > @
 
 # Test.
 [] > compares-two-different-types
   not. > @
     eq.
-      TRUE
+      true
       42
 
 # Test.
diff --git a/eo-runtime/src/test/eo/org/eolang/goto-tests.eo b/eo-runtime/src/test/eo/org/eolang/goto-tests.eo
index 8c0c64923..fd9c35a37 100644
--- a/eo-runtime/src/test/eo/org/eolang/goto-tests.eo
+++ b/eo-runtime/src/test/eo/org/eolang/goto-tests.eo
@@ -43,7 +43,7 @@
                   if
                     i.as-int.lt 10
                     g.backward
-                    TRUE
+                    true
           stdout "Finished!\n"
           i
       10
@@ -62,7 +62,7 @@
               *
                 if
                   x.eq 0
-                  g.forward TRUE
+                  g.forward true
                   TRUE
                 r.write (42.div x)
         (dataized r).as-bytes > result
diff --git a/eo-runtime/src/test/eo/org/eolang/memory-tests.eo b/eo-runtime/src/test/eo/org/eolang/memory-tests.eo
index 0c7eb2de4..1d89363dd 100644
--- a/eo-runtime/src/test/eo/org/eolang/memory-tests.eo
+++ b/eo-runtime/src/test/eo/org/eolang/memory-tests.eo
@@ -112,7 +112,7 @@
       and. > @
         QQ.io.stdout e
         m.free
-    TRUE
+    true
 
 # Test.
 [] > memory-is-strictly-typed-string-error-overflow
diff --git a/eo-runtime/src/test/eo/org/eolang/negative-infinity-tests.eo b/eo-runtime/src/test/eo/org/eolang/negative-infinity-tests.eo
index 9a5fbfd90..2c747d0e9 100644
--- a/eo-runtime/src/test/eo/org/eolang/negative-infinity-tests.eo
+++ b/eo-runtime/src/test/eo/org/eolang/negative-infinity-tests.eo
@@ -76,7 +76,7 @@
 [] > negative-infinity-lt-positive-infinity
   eq. > @
     negative-infinity.lt positive-infinity
-    TRUE
+    true
 
 # Test.
 [] > negative-infinity-not-lt-nan
@@ -100,13 +100,13 @@
 [] > negative-infinity-lte-negative-infinity
   eq. > @
     negative-infinity.lte negative-infinity
-    TRUE
+    true
 
 # Test.
 [] > negative-infinity-lte-positive-infinity
   eq. > @
     negative-infinity.lte positive-infinity
-    TRUE
+    true
 
 # Test.
 [] > negative-infinity-not-lte-nan
@@ -118,13 +118,13 @@
 [] > negative-infinity-lte-int
   eq. > @
     negative-infinity.lte 42
-    TRUE
+    true
 
 # Test.
 [] > negative-infinity-lte-float
   eq. > @
     negative-infinity.lte 42.5
-    TRUE
+    true
 
 # Greater than.
 [] > negative-infinity-gt-negative-infinity
diff --git a/eo-runtime/src/test/eo/org/eolang/positive-infinity-tests.eo b/eo-runtime/src/test/eo/org/eolang/positive-infinity-tests.eo
index 43dd2ca6a..e6d5cf2c4 100644
--- a/eo-runtime/src/test/eo/org/eolang/positive-infinity-tests.eo
+++ b/eo-runtime/src/test/eo/org/eolang/positive-infinity-tests.eo
@@ -100,7 +100,7 @@
 [] > positive-infinity-lte-positive-infinity
   eq. > @
     positive-infinity.lte positive-infinity
-    TRUE
+    true
 
 # Test.
 [] > positive-infinity-not-lte-negative-infinity
diff --git a/eo-runtime/src/test/eo/org/eolang/seq-tests.eo b/eo-runtime/src/test/eo/org/eolang/seq-tests.eo
index 9709c88d8..1a75d456c 100644
--- a/eo-runtime/src/test/eo/org/eolang/seq-tests.eo
+++ b/eo-runtime/src/test/eo/org/eolang/seq-tests.eo
@@ -82,51 +82,51 @@
 # This test should have acceptable time to pass.
 [] > very-long-seq
   eq. > @
-    TRUE
+    true
     seq
       *
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
-        TRUE
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
+        true
 
 # Test.
 [] > seq-single-dataization-int-equal-to-test
diff --git a/eo-runtime/src/test/eo/org/eolang/string-tests.eo b/eo-runtime/src/test/eo/org/eolang/string-tests.eo
index de055d390..6d421fe30 100644
--- a/eo-runtime/src/test/eo/org/eolang/string-tests.eo
+++ b/eo-runtime/src/test/eo/org/eolang/string-tests.eo
@@ -148,7 +148,7 @@
     eq.
       "x"
       "x"
-    TRUE
+    true
 
 # Test.
 [] > one-symbol-string-compares
@@ -240,7 +240,7 @@
         1
     [e]
       QQ.io.stdout e > @
-    TRUE
+    true
 
 # Test.
 [] > slice-end-below-start
@@ -252,7 +252,7 @@
         -1
     [e]
       QQ.io.stdout e > @
-    TRUE
+    true
 
 # Test.
 [] > slice-end-greater-actual
@@ -264,4 +264,4 @@
         5
     [e]
       QQ.io.stdout e > @
-    TRUE
+    true
diff --git a/eo-runtime/src/test/eo/org/eolang/switch-tests.eo b/eo-runtime/src/test/eo/org/eolang/switch-tests.eo
index 715407ca3..e235079c7 100644
--- a/eo-runtime/src/test/eo/org/eolang/switch-tests.eo
+++ b/eo-runtime/src/test/eo/org/eolang/switch-tests.eo
@@ -35,7 +35,7 @@
           FALSE
           "1"
         *
-          TRUE
+          true
           "2"
     "2"
 
@@ -62,13 +62,13 @@
     switch
       *
         *
-          TRUE
+          true
           "TRUE1"
         *
           FALSE
           "FALSE"
         *
-          TRUE
+          true
           "TRUE2"
     "TRUE1"