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diff --git a/lua/chupacabra/refcard.md b/lua/chupacabra/refcard.md
index daaa7ae..a2b473c 100644
--- a/lua/chupacabra/refcard.md
+++ b/lua/chupacabra/refcard.md
@@ -10,6 +10,7 @@ Chupacabra is a stack-based programming language/calculator implemented in lua.
 - **Arrays**: You can push arrays onto the stack. For example, `[1 2 3 4]` pushes the array {1, 2, 3, 4} onto the stack.
 - **`.`**: The `.` operator pops the top element from the stack and discards it.
 - **`:`**: The `:` operator duplicates the top element of the stack
+- **`?`**: The `?` operator swaps the top two elements of the stack
 
 ## Array-first keywords
 - **`@`**: the `@` keyword allows you to grab a specific value from an array by index, e.g. `[10 20 30] 2 @` would return the value `20`.