Add OP_LESSTHAN page

Author: thunderbiscuit

.vitepress/config.js

@@ -172,7 +172,7 @@ export default {
         { text: "<code>156 | OP_NUMEQUAL</code>", link: "/opcodes/OP_NUMEQUAL.md" },
         { text: "<code>157 | OP_NUMEQUALVERIFY</code>", link: "/opcodes/OP_NUMEQUALVERIFY.md" },
         { text: "<code>158 | OP_NUMNOTEQUAL</code>", link: "/opcodes/OP_NUMNOTEQUAL.md" },
-        { text: "<code>159 | 🚧 OP_LESSTHAN</code>", link: "/opcodes/OP_LESSTHAN.md" },
+        { text: "<code>159 | OP_LESSTHAN</code>", link: "/opcodes/OP_LESSTHAN.md" },
         { text: "<code>160 | 🚧 OP_GREATERTHAN</code>", link: "/opcodes/OP_GREATERTHAN.md" },
         { text: "<code>161 | 🚧 OP_LESSTHANOREQUAL</code>", link: "/opcodes/OP_LESSTHANOREQUAL.md" },
         { text: "<code>162 | 🚧 OP_GREATERTHANOREQUAL</code>", link: "/opcodes/OP_GREATERTHANOREQUAL.md" },

opcodes/OP_LESSTHAN.md

@@ -1,5 +1,78 @@
-# Work In Progress
+# OP_LESSTHAN
 
-:::warning
-This page has not yet been written. If you have experience with bitcoin Script and would like to contribute, please do! You can open a PR [on the repository for this website](https://github.com/thunderbiscuit/opcode-explained).
+:::info
+**Opcode number:** 159  
+**Byte representation:** `0x9f`  
+**Short description:** Pop the top two items; push 1 if the second is less than the top, 0 otherwise.
 :::
+
+`OP_LESSTHAN` compares the top two items on the stack as integers. If the second item is less than the top item, it pushes `1` (`true`) onto the stack. If not, it pushes an empty array (`false`). Both items are removed from the stack after the comparison.
+
+### Operation
+
+1. Take the top item (`a`) and the second item (`b`) from the stack.
+2. Compare the two items:
+   - If `b < a`, push `1` (`true`) onto the stack.
+   - Otherwise, push an empty array (`false`) onto the stack.
+3. Remove the original items (`a` and `b`) from the stack.
+
+### Notes
+
+- Both items must be valid integers. Bitcoin Script interprets byte arrays up to **4 bytes** as integers.
+- An empty array (`[]`) is treated as `0` when compared.
+- If there are fewer than two items on the stack when `OP_LESSTHAN` is executed, the script will fail.
+
+---
+
+## Examples
+
+### Example 1: Second item is less than the top item
+
+```shell
+# ASM script
+OP_2 OP_3 OP_LESSTHAN
+
+# Raw script
+52539f
+
+# Stack (before OP_LESSTHAN)
+3  # top
+2
+
+# Stack (after OP_LESSTHAN)
+1  # true, as 2 < 3
+```
+
+### Example 2: Second item is greater than the top item
+
+```shell
+# ASM script
+OP_3 OP_2 OP_LESSTHAN
+
+# Raw script
+53529f
+
+# Stack (before OP_LESSTHAN)
+2  # top
+3
+
+# Stack (after OP_LESSTHAN)
+[]  # false, as 3 is not less than 2
+```
+
+### Example 3: Comparing two zeros
+
+```shell
+# ASM script
+OP_0 OP_0 OP_LESSTHAN
+
+# Raw script
+00009f
+
+# Stack (before OP_LESSTHAN)
+[]  # top
+[]
+
+# Stack (after OP_LESSTHAN)
+[]  # false, as 0 is not less than 0
+```